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First Examples of a Claisen Rearrangement Stereocontrolled by a Sulfinyl Group Synthesis of Novel -Sulfinyl Dithioesters.

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tion caused by electronegative atoms in the K system. There are
broad similarities in relative efficiency for 7 with that for p (for
which the series 1 < 2 < 3 < 4 < 6 = 7 < 8 < 5 was obtained from
hyper-Rayleigh scattering measurements at 1064 nm),f3b1consistent with a “cascade” effect, although the relative ordering is
not identical; significant differences in chromophore N L O efficiency between quadratic and cubic responses for this series of
complexes are the small y for the imino-linked 8 relative to its
high /j value. and the large y for the yne-linked 7 in contrast to
its more modest /3 value. Complex 8 is the only one in this series
for which the imaginary part of 7 is larger than the real part,
suggesting proximity of 2 w to the two-photon absorption peak
and strong dispersion effects-possibly resulting in a diminished
real part of ;’. The disparity of the results for 7 suggests that
different alkynyl ligands may be required for optimization of
quadratic and cubic NLO efficiencies in organometallic complexes.
The effect of the ligated metal upon /3 and y values differs.
Quadratic nonlinearities for alkynyl(cyclopentadienyl)bis(tripheny1phosphane)ruthenium complexes are three to five times
larger than those for the corresponding alkynyl(tripheny1phosphane)gold complexes,[3bJconsistent with the fact that the 18electron, more easily oxidizable ligated ruthenium(i1) center is a
better donor than the 14-electron, less readily oxidizable ligated
gold(1) center. In contrast, cubic nonlinearities for the “extended
chain” alkynyl(tripheny1phosphane)gold complexes 5 and 7
are, in absolute terms, two to three times larger than those for
the (cyclopentadienyl)bis(triphenylphosphane)ruthenium analogues, despite both the nominally greater delocalization (and
hence polarization) possibilities due to the cyclopentadienyl
group and additional triphenylphosphane ligand and the substantial dispersion enhancement of the Ru complex. This suggests that
different ligated metals may be required to optimize quadratic
and cubic N LO efficiencies in organometallic complexes.
Data from investigations of the cubic molecular optical
nonlinearities of organometallic complexes have been summarized.12.41The largest reported nonlinearities (up to 4933 x
10 3h esu) are for oligomeric systems,”’ and it is generally accepted that chain lengthening by oligomerization and polymerization leads to an increase in value. The nonlinearities of 5
and 7 are the largest yet for a monomeric organometallic compound and approach the largest values known for oligomeric
organometallic systems. The presence of the metal atom terminating the alkynyl ligand in these organometallic chromophores
is critical for their NLO response-precursor acetylenes have
nonlinearities not significantly different from that of the solvent-- -but it is possible that one metal may suffice. (Alkyny1)metal oligomers and polymers are currently attracting a great
deal of attention because of their potential NLO p e r f ~ r m a n c e , ~ ’ ~
but it is possible that metal-capped organic oligomers o r polymers may also be worthy of study.
Experimen tul Sect ion
Measurements were performed at 800 nm with a system consisting of a Coherent
Mira Ar-pumped Ti-sapphire laser that generates a mode-locked train of approximately 100fs pulses and a Ti-sapphire regenerative amplifier pumped with a frequrncydoubled. Q-switched pulsed YAG laser (Spectra Physics GCR) at 30 Hzand
employing chirped pulse amplification. T H F solutions were examined in a glass cell
with a 0.1 cm path length The 2-scans were recorded a t two concentrations for each
compound. and the real and imaginary part of the nonlinear phase change determined by numerical fitting “” The real and imaginary part of the hyperpolarizability
of the solute was then calculated assuming linear concentration dependence. The
nonlinearities and light intensities were calibrated against measurements of a 1 mm
23 x
cm2W - I
thick silicii plate for which the nonlinear refractive index i ~=
was assumed
Received: August 20,1996 [Z9475IE]
German version: Anxew. Chem. 1997, 109. 386-388
An,eeir. (%em. I n i .
E d Eiql. 1997, 36, No. 4
C
Keywords: alkyne complexes * gold
- nonlinear optics
a) H. S. Nalwa, Appl. Orgunornet. Chem. 1991. 5 , 349; h ) N. J. Long, Angeu.
Chem. 1995. 107. 37: Angew. Chem.. In!. Ed. EngI. 1995. 34. 21
S . R. Marder in Inoi-gunic Marerruls (Eds.: D. W Bruce. D O’Hare). Wiley,
Chichester, 1992. p. 115
For reports ofg values for alkynylmetal complexes, see a ) 1 R. Whittall. M. G .
~ ~ ~ IS. 1935; b)
Humphrey, A Persoons, S. Houbrechts. O r g u n o m r ~ u l l i1996.
1. R. Whittall. M. G . Humphrey. S. Houbrechts. A. Persoons. D. C. R. Hockless, Orgonometullics 1996, 15. 5738.
a) S. Ghosal, M. Samoc, P. N. Prasad. J. J. Tufariello. J. ( % e m Ph,u. 1990, 94,
2847; b) L. K. Myers, D. M Ho, M E. Thompson. C. Lmghoff, Polyhedron
1995. 14. 57; c) I. R. Whittall, M. G. Humphrey. M. Sarnoc. J. Swiatkiewicz,
B. Luther-Davies. Orgunomrrullics 1995. 14. 5493
a) R Cross. M. F. Davidson. A. J McLennan. J Orgnnonicr. Cliem 1984. 265.
C37; b) M. 1 Bruce, E. Horn. J. G. Matisons, M. R. Snow. . l u s i . J. Chem. 1984,
37. 1163
M. Sheikh-bahae. A. A. Said, T. Wei. D. J. Hagan. E W. van Stryland. IEEE J.
Quuntuni Elerrroii. 1990. 24, 760.
a) M. G . Kuzyk. C. W. Dirk, P / y . Ret,. A 1990, 41 5098: b) C W. Dirk. L.-T.
Cheng, M. G . Kuzyk. In,. J. Quunfum Chem 1992. 43. 27. c ) C. W. Dirk, N.
Cahallerro. M. G . Kuzyk, Cheni. Muter. 1993, 5, 733.
P. L. Porter, S. Guha, K. Kang, C. C Frazier. Polj.mer 1991. 32. 1756.
a) A. P. Davey. D. J. Cardin, H . J. Byrne, W. Blau in O r p i n k Molecules for
Nonhnear 0ptic.s und Photonics (Eds.: J. Messier. F. Kajzar, P. Prasad). Kluwer.
Dordrecht, 1991, p 391; b) S. Guha, C . C . Frazier. W. P Chen. P. Porter, K.
Kang. S E. Finberg, SPIE-lnr. Sot. Opr. Eng. 1989. Il0.T. I S
First Examples of a Claisen Rearrangement
Stereocontrolled by a Sulfinyl Group:
Synthesis of Novel ol-Sulfinyl Dithioesters
Carole Alayrac, Christophe Fromont,
Patrick Metzner,* and Nguyen Trong Anh
Sulfoxides are very useful chiral auxiliaries in asymmetric
synthesis.“. The efficient control of the stereochemistry in the
Diels-Alder reactions[31with unsaturated sulfoxides as chiral
dienophiles prompted us to consider the sulfinyl moiety as an
auxiliary for asymmetric [3,3] sigmatropic shifts.[41Induction by
an asymmetric carbon center located outside the sigmatropic
framework has been previously demonstrated,[’, but the use of
a stereogenic sulfur center is unprecedented. However, we were
concerned about a subsequent p-elimination of the sulfinyl
group”] from the expected y-unsaturated a-sulfinyl carbonyl
compounds. We therefore chose to perform the Claisen rearrangements with the thiocarbonyl analogues. This transposition
occurs at much lower temperatures than for the oxygen analogues-usually at room temperature and in neutral medium.]’. ’I Further interest in this reaction arises because the thiocarbonyl functional group can be converted into sulfurfree functional groups such as carbonyl or alkoxycarbonyl
groups.[’. ’‘1 We report here the first examples of asymmetric
thio-Claisen rearrangements directed by a sulfinyl group.
[*] Dr. P. Metzner, Dr. C. Alayrac, C. Fromont
Laboratoire de Chimie Moleculaire et Thio-organique (Associe a u CNRS)
ISMRA-Universite
6 blvd du Marechal Juin, F-14050 Caen (France)
Fax: lnt. code f23145-2877
e-mail: metzner(u unicaen.fr
Dr. N. T. Anh
Laboratoire des Mecanismes Reactionnels (Associe au CNRS)
Ecole Polytechnique
F-91128 Palaiseau (France)
V C H Verlugsgesellschufi mhH. 0-69451 Weinheim.1997
0570-0&’33/97/3604-0371$15.00+ .25jO
371
COMMUNlCATlONS
The substrates of the rearrangement are ketene dithioacetals
containing a sulfinyl group at the double bond. They were readily prepared from 2-sulfinylethanedithioates. The synthetic utility of a-sulfinyl ketones and esters has been reviewed.['a,
These molecules, for example, provide very high asymmetric
induction in carbonyl
l b l and in aldol-type condensations.[' ']In contrast, molecules bearing a sulfinyl group
adjacent to a thiocarbonyl function have so far received little
attention.[". 13] We chose to study four different alkylsulfinyl
groups with varied steric hindrance (R' = methyl, isopropyl,
cyclohexyl, tert-butyl) and work exclusively with racemic compounds.
The a-sulfinyl dithioesters 2 were prepared by adding methyl
4-fluorophenyltrithiocarbonate to lithiated alkyl methyl sulfoxides 1 in tetrahydrofuran at -40 "C (Scheme 1). Deprotonation
action times range from 5 to 45 hours according to the nature of
R'. The crude yields are greater than 90%. The yields after
purification by chromatography on silica gel are lower due to a
partial decomposition of the product. However, as the purity of
crude dithioesters 4 is satisfactory, no purification is necessary
to carry out the next step.
The diastereomeric ratio was determined by measuring the
integrals of 'H NMR signals of the MeS group of each isomer
(Table 1).[I6] This demonstrated that the asymmetric induction
Table 1. Diastereoselective Claisen rearrangement of compounds 3 according to
Scheme 2.
3
R'
R2
t [a]
Ihl
4
H
5
12
24
Me
45
H
12
12
20
24
4a,
4a,
4b,
4b,
4c,
4.2,
4d,
4d,
H
Me
Me
H
Me
PI
Yield [c]
["/I
93
94
98
299
94
199
95
299
7
6
2
1
6
1
5
1
63
51
40
50
42
50
41
60
3bl: R' = Bu,R2 = H
[a] The rearrangements were performed at room temperature in CH,CI, and monitored by 'H NMR spectroscopy and thin-layer chromatography. [b] Diastereomeric
ratio according to 'H NMR analysis. Only compounds 4a, and 4a, underwent
significant isomerization on silica gel. [c] Yield of isolated product.
3b2: R1 = Bu, R2 =Me
3Cl: ~
1 iPr.
= ~2 = H
313: R 1 = Pr, R2 = Me
DMSO
e ) MuLi
3a
1) MeSCSpMe
3dl:R' = C-C&11, R2 = H
3d2: R1 = C - c ~ H 1 1 ,R2 =Me
3al: R1 = Me, R2 = H
%:R1=
R2=Me
R2
d) A
x
Scheme 1. Preparation of compounds 3a-d. 1, 2: a, R' = Me, b, R' = rBu, c.
R' = iPr, d, R' = c-C,H, I ; Ar = 4-fluorophenyl; X = Br, I.
of 2 by lithium diisopropylamide (LDA) was quantitative and
predominantly led to the cis enethiolateI2.*, l4l (isomeric ratio
> 9: l).[15] The cis enethiolization is typical of thiocarbonyl
compounds"] and contrasts the trans enolization of esters and
ketones (under aprotic conditions). It is most probably increased for 2 by the assistance of lithium coordination to the
sulfinyl oxygen atom. Enethiolates are ambident nucleophiles
that react through the sulfur termini with alkyl halides. Thus,
ketene dithioacetals 3 were obtained by S-allylation of the
enethiolates resulting from deprotonation of 2. As the dithioester 2a (R' = Me) is not stable, the corresponding ketene
dithioacetals were prepared in a single step from dimethylsulfoxide (DMSO) by using the method applied by Yokoyama et
al.[' 21 (Scheme 1).
Ketene dithioacetals 3 readily rearrange at room temperature
into y-unsaturated cc-sulfinyl dithioesters 4 (Scheme 2). The re-
(2S',SS)-4a,c-d
( 2 S S F T )-4b
Scheme 2. Claisen rearrangement of compounds 3. For groups R' and R2 see
Table 1
372
0 VCH
Verlugsgeseltschufl mbH. 0-69451 Weinheim. 1997
of sulfoxides was extremely effective: in all cases a very high
diastereoselectivity was measured (diastereomeric ratio
>93:7). Interestingly, the steric demand of R' seems to have
little influence on the selectivity. We could also demonstrate that
the rearrangement does not proceed under thermodynamic control. Indeed the dithioesters 4 c isomerize on treatment with
triethylamine at room temperature, and the ratio at equilibrium
is 4:l. The configuration of the major diastereomer of
dithioester 4a, (R' = R2 = Me) has been assigned as (2S*,SS*)
by X-ray ~rystallography.~'~~
According to similar trends observed in 'H NMR spectra, the same configuration can be empirically assigned to the major isomers of the other Claisen
rearrangement products.['
To rationalize our results, we suggest a model that is a natural
extension of the Felkin one. Since the main physical phenomenon in a reaction between ions is electron transfer from the
nucleophile to the electrophile, in nucleophilic (electrophilic)
additions, the best acceptor (donor) should be placed anti to the
incoming nucleophile (electrophile) .[''I In the present case, the
lone pair of electrons of the sulfinyl group of 3 is the best electron donor. Consequently the attack of the allylic chain should
occur anti to this lone pair of electrons.f201Thus, two transition
states derived from the conformers A and B are conceivable for
the major ( 2 )ketene dithioacetal3 (Scheme 3 ) . The former (A)
is more favored as the alkyl group R' is bulkier than the oxygen
atom. This is in agreement with the observed stereochemistry
(2S*,SS*). Moreover, in model A, the R' group occupies an
outside position, which may explain the slight influence of its
size on the observed selectivity. The same model applied to the
minor ( E )isomer leads to the same (2S*,SS*) diastereomer.[211
Calculations are underway to evaluate the reliability of this
model.
In conclusion, we have described a new method for asymmetric C-C bond formation in acyclic compounds. The Claisen
rearrangement of ketene dithioacetals bearing a sulfinyl group
requires mild conditions and is highly diastereoselective. Furthermore, no elimination of the sulfinyl group was observed. In
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Angew. Chem. In!. Ed. Engl. 1997, 36, No. 4
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SMe
the residue by columnchromatography (silica gel. petroleumetherjethyl acetate 7/3)
afforded 38 mg of dithioester 4 d , (47%, ratio of diastereomers = 93:7). 4 d , :
Orange solid, m.p. 37°C; 'H NMR (CDCI,, 250 MHz): 6 = 1 25-2.03 (m. lOH),
2.56(tt,J=3.6,12.0Hz,lH),2.68(~,3H),3.00-3.06(m,2H).4.39(dd,
J = 4.6,
10.2 Hz, l H ) , 5.05-5.17 (m, 2H), 5 62-5.78 (m, I H ) ; I3C NMR (CDCI,.
62MHz):6=19.8.21.9,25.3,28.4,26.0,28.5,36.5,554,76.3. 118.8,132.5,228.5;
IR(NaCI):C = 2930,2854,1450,1418, 1054,992,946,920cme1: MS:m/z(%).276
(0.5) [ M ' ] . 91 (18). 83 (52), 82 (lo), 81 (27). 55 (loo), 47 (17). 43 (19), 41 (89);
elemental analysiscalcd. for C,,H,,OS,: C 52.13, H 7.29, S 34.79; found: C 52.07,
H 7.20. S 34.60; ' H N M R signal of the minor isomer (CDCI,): 6 = 2.70 (s, 3 H ) .
Received: September 2.3. 1996 [294871E]
German version: Angew. Chem. 1997. 109, 418-420
Keywords: C-C coupling * chiral auxiliaries
rearrangements sulfoxides
-
-
dithioesters
-
a) M. C. Carrerio, Chem. Rev. 1995, 95. 1717-1760; b) G. Solladie, M. C.
Carrefio in Organosulfur Chemistry-Synthetrc Aspects, Voi. 1 (Ed.: P. C B.
0
Page). Academic Press, London, 1995, pp. 1-47; c) G. Solladie in Perspectives
in the Orgunic Chemistry of Sulfur (Stud. Org. Chem. 1987.28). pp. 293-314,
(2R,SS)-4a,c-d
d) A. J Walker, Terruhedron: Asymmetry 1992, 3, 961 -998; e) G. Posner, 2.
( 2 R , S f f ) - 4b
Rappoport, C. Stirling in The Chemistry of Sulphones und Sulphoxides-The
Scheme 3. Considerations of the stereochemical course of the Claisen rearrangeChemistry of Functionul Groups (Ed: S . Patai), Wiley. Chichester. 1988, pp.
ment of compounds 3.
823-849; f) J. L. Garcia Ruano, Phosphorus Surfur Silicon Relut. Elem. 1993,
74, 233-247.
P. Metzner, A. Thuillier, Sulfur Reagents in Organic Synfhesi.v. Academic Press,
London, 1993.
contrast the rearrangement products in the oxygen series could
a) C. Maignan, A. Guessous, F. Rouessac, Tetrahedron L e t / . 1984, 25, 1727not be isolated because higher temperatures were necessary for
1728; b) T. Koizumi, PhosphorusSulfur Silicon Relat. Elem. 1991.58. 111 - 127;
c) B. Ronan, H. B. Kagan. Tetrahedron: Asymmetrv 1991. 2, 75-90
the Claisen rearrangement."] To the best of our knowledge the
Review. D. Enders, M. Knopp, R. Schiffers. Tetruhedron. A.s~mmctry1996, 7,
reaction presented here is the first [3,3] rearrangement directed
1847- 1882
by a sulfinyl group. Application of this method to enantiopure
J. K. Cha, S. C. Lewis, Tetruhedron Lett. 1984, 25, 5263-5266; M. J. Kurth.
substrates and elaboration of carbon chains bearing three conC.-M. Yu, ibid. 1984,25,5003-5006; S. Hatakeyama, K. Saijo. S. Takano, ibid.
1985,26.865-868; M. Balestra, J. Kallmerten. ibid. 1988,29,6901-6904;S. D.
tiguous stereogenic centres are in progress.
Kahn, W. J. Hehre, J. Org. Chem. 1988,53,301-305; R. Briickner, H. Priepke.
Angew. Chem. 1988. 100, 285-286; Angew. Chem. Int. Ed. Engl. 1988. 27.
Experimental Sect ion
278-279; S. Desert. P Metzner, M. Ramdani, Tetrahedron 1992, 48, 1031510 326.
Sulfoxides 1 were prepared in two steps from the corresponding thiols according to
P. Beslin, S. Perrio, J Chem. Soc. Chem. Commun. 1989,414-416; Tetruhedron
known procedures [22]
1991,47,6275-6286.
2 d : MeLi(9.0 mL of a 1 . 6 solution
~
in ethyl ether, 14.4 mmol) was added dropwise
R C. Cookson, R. Gopalan. J Chem. SOC.Chem. Commun. 1978,608; G . H.
to a solution of I d (2.24 g, 14.4 mmol) in T H F (60 mL) at -4O'C. The reaction
Posner, R. D. Crouch. C. M. Kinter. J.-C. Carry, J. Org. Chem. 1991, 56,
mixture was stirred for 40 min at - 30 'C then cooled to - 40 "C, and a solution of
6981 -6987; LM.Vatele, Tetrahedron Lert. 1983, 24, 1239- 1242.
methyl 4-fluorophenyltrithiocarbonate(1.57 g, 7.2 mmol) in T H F (6 mL) was
P Metzner. Sj'nthe.~is1992, 1185-1 199.
added. The resulting mixture was stirred for 1 h at - 20 "C then allowed to warm up
P. J. W. Schuijl, L Brandsma, R e d . Truv. Chim. fays-Bus 1968, H7, 929-939;
to 0 - C . It was worked up by addition of saturated aqueous NH,CI solution
P. Metzner, T. N. Pham, J. Vialle, Nouv. J. Chim. 1978, 2, 179-182
(20 mL), followed by extraction with CH,CI, (3 x 30 mL). The combined organic
H. Tdkahashi, K. Oshima, H. Yamamoto, H. Nozaki, J. Am. Chem. SOC.1973,
layers were washed with brine. dried over MgSO,, and then concentrated to dry95, 5803-5804.
ness. Purification of the i-esidue by column chromatography (silica gel, petroleum
G. Solladie, Synthesis 1981,188- 196; C. Mioskowski, G . Solladie. Tetrahedron
etherjethyl acetate 1 1) afforded 0.93 g of dithioester 2 d ( 5 5 % ) . 2d: Orange solid.
1980.36. 227-236.
m p. 4 3 ' C ; ' H NMR (CDCI,. 250 MHz): 6 =1.18-2.15 (m. IOH), 2.70 (s, 3H).
M. Yokoyama, K. Tsuji. M. Hayashi, T. Imamoto. J. Chent. Sot. ferkrn Truns.
2.75 (tt, J = 3.6. 1 1 5 Hz, 1 H). 4.32 and 4.37 (AB, JAB
= 12.5 Hz. 2H); I3C NMR
11984. 85-90.
(CDCI,. 62 MHz): d = 21.1. 24.0, 25.2, 25.5, 25.6, 26.9, 58.5, 68.8, 222.8. IR (NaAloup. D. Farge. C. James, S. Mondot, I. Cavero. Dru,q.s of the Future
CI): B = 3424.2930.2852.1648.1448, 1414,1264, 1202,1124,1054.970,730cm~';
1990, 15. 1098-1108; JLC. Aloup, J. Bouchaudon. D. Farge. C. James. J.
MS: m i - ( % ) : 236(0 8) [ M t ] . 106(18). 91(14), 84(12), 83(15), 8117). 73(32),
Deregnaucourt, M. Hardy-Louis, J Med. Chem. 1987, 30, 24-29; M.
61(59). 59(31). 88(67). 58(96).48(11),47(28). 45(42),43(33),41(100);elemental
Cinquini. A Manfredi, H. Molinari, A. Restelli, Tetruhedron 1985, 41, 4929analysis calcd for C,H,,OS,: C 45 72, H 6.82, S 40.69, found: C 45.80, H 6.86, S
4936.
40 39
The designation cis refers to the relationship between the sulfinyl and the SLi
3 d , : A solution of Zd (342 mg, 1.45 mmol) in T H F ( 5 mL) was added to a solution
groups.
of LDA (1.57 mmol) in T H F [5 2 mL, freshly prepared from nBuLi (1 mL of a I .6 N
In previous work from our laboratories, we havedemonstrated that enethioldte
solution in hexane) and diisopropylamine (0.25 mL)] at -40'C. After the solution
alkylation proceeded with complete retention of configuration [23]. The conhad been stirred for 40 min at - 30 -C. it was cooled to - 40 -C and ally1 bromide
figurations of ketene dithioacetals were assigned based on the results of NOE
(0.16 mL, 1.9 mmol) was added The reaction mixture was allowed to warm to 0 ' C
difference studies. which were carried out on the corresponding S-benzyl
over 1.5 h then treated with saturated aqueous NH,CI solution (10 mL). The
ketene dithioacetals.
product was extracted with CH,CI, (3 x 10 mL); the combined organic layers were
In order to determine the ' H NMR signals corresponding to the minor isomer,
washed with brine. dried over MgSO,, and then concentrated to dryness for analy:omoounds 4 were submitted to a deDrOtOndtiOn/DrOtOnatiOnseouence with
sis. The crude product was obtained with quantitative yield (400 mg). 3 d , : Signals
different bases (NEt,, NaH). Once we had the reference spectrum of the minor
that were clearly identified, ' H NMR (CDCI,, 250 MHz):
of the major isomer (2)
isomer. it was possible to evaluate the isomeric ratio of crude compounds 4 by
b = 2.10-2.15 (m, 1 H). 2.42 (s. 3 H), 3.48 and 3 68 (AB signals of an ABX system,
expanding the area containing the 'H NMR signals of the MeS groups and by
JA,=13.4Hz.J,,=7.9Hz, JB,=7.0Hz,2H),5.14-5.27(m,2H),8.80-5.92(m,
measuring the integrals of both singlets.
1 H), 6.09 (s. 1 H): signals ofminor isomer ( E )that were clearly identified; ' H NMR
[17] 4 a , : C,H,,OS,; triclinic, space group PI, u =7.617(4). h = 8.499(5).
(CDC1,)- ii = 2.09-2 14 (m. 1 H). 2.45 (s. 3 H), 3.52 (dd, J = 1 .I. 6.7 Hz. 2H). 5.22
L' = 9.576(4) A,z = 80.18(2),p = 80.75(2), 7 = 68 74(2);, V = 566.0 ( 5 ) A
',
(dd, J = 1 . 0 . 10.0Hz. IH),5.27-5.35(m. l H ) . 5 8 4 ( d d t , J = 6 . 7 . 10.0. 17.0Hz,
2 = 2, M,,,,, = 222.4. p =1.305 Mgm-3. Siemens P3jPC diffrdctomer, Mo,,
1 H). 6 19 (s. 1 H)
radiation (highly oriented graphite crystal monochromator. i = 0 71073 A).
4 d , : Claisen rearrangement of 3d, (80 mg, 0.29 mmol) was carried out in CH,CI,
The structure was solved by using Siemens SHELXTL PLUS (PC version) and
(3 mL) at room temperature and monitored by thin-layer chromatography. It was
refined by the full-matrix least-squares method Absorption coefficient
complete after 20 h. The solution was then concentrated to dryness. The 'H NMR
0.61 1 mm- ', 28 range 3 0 to 56 0 , scan type Oj28, scan range ( w ) 2.30'.
temperature 173 K, two standard reflections measured ever1 98 reflections,
spectrum showed that the ratio of the two diastereomers was 95:5. Purification of
Angew. Chcm. In!. ELI.E n , d 1997.36. No. 4
G
VCH Verlagsgrsellschuft mbH, 0-69451 Wemherm, 1997
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373
COMMUNICATIONS
2663 collected reflections, 2464 independent reflections, 21 79 observed reflections, no absorption corrections applied, 165 refined parameters, isotropic
refinement, R = 0.0375, ( R , = 0.0574). Crystallographic data (excluding
structure factors) for the structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-179-147. Copies of the data can be obtained free of charge on
application to The Director, CCDC, 12 Union Road, Cambridge CB2 lEZ,
UK (fax: Int. code +(1223) 336-033; e-mail. deposit@chemcrys.cam.ac.uk)
[IS] Systematic investigation of NMR spectra shows that the chemical shifts of the
proron linked to the stereogenic center and of the MeS group of the minor
isomer occur downfield relative to that of the major isomer.
[19] N. T. Anh. 0. Eisenstein, Nouv. J. Chim. 1977, f.61 -70; N. T. Anh. F. Maurel.
J.-M. Lefour, New J. Chem. 1995, 19, 353-364; N. T. Anh, Orhitales,fiontiere.s
- Manuelpratique, InterEditions CNRS Editions, Paris, 1995.
[20] An analogous model has been proposed to explain the outcome of a-sulfinyl
enolate alkylation; M. FUjita, M. Ishida, K. Manako, K Sato, K. Ogura.
Tetrahedron Letr. 1993, 34, 645-648
[21] Preliminary results obtained from a E / Z mixture of compound 3d,
(R' = cC,H,,, RZ = H) containing predominantly the E isomer show that
there is an independency between the configuration of the ketene dithioacetal
and rearrangement selectivity (cf. ref. 161).
[22] A. W Herriott, D. Picker, Synthesis 1975,447-448; C. R Johnson. J. E. Keiser, Org. Synth. 1966, 46, 78-80.
[23] P. Beslin, P. Metzner, Y Vallee. J. Vialle, Tetruhedron Lett. 1983, 24, 36173620; P. Beslin, Y. Vallee, Tetrahedron 1985, 41, 2691-2705.
Unusually Stable Organomercury Hydrides and
Radicals**
Eiichi Nakamura,* Yong Yu, Seiji Mori, and
Shigeru Yamago
There is growing interest in the characterization of organomercury hydrides,"] which have been elusive species until very
recently. Hydride reduction of organomercury chlorides is an
important method for generating carbon radicals.[21The reaction is considered to proceed in three steps: formation of an
organomercury hydride, homolysis of the Hg-H bond, and
immediate decomposition of the transient organomercury radicaLL3]However, experimental evidence for this proposed mechanism has been rather scant. A few alkylmercury hydrides were
recently isolated and proved to be very unstable.["] The second
intermediate, an organomercury radical, has still remained elusive, and no direct proof of its existence has been obtained. Here
we report on the synthesis of the unusually stable organomercury hydrides 3 and deuterides 3D, which are much more stable
than the mercury hydrides described so far. Furthermore, these
hydrides generate the organomercury radicals 6, which are
stable enough to be trapped intermolecularly.
The reaction of cyclopropenone acetal lat4]with Hg(OAc), ,
followed by treatment with a saturated NaCl solution, stereospecifically produced the (2)-olefinic mercury chloride 2ax in
92% yield. The mercury chlorides 2 with different R2 groups
could also be prepared.''] Stereospecific conversion of the mercury chlorides to the hydrides 3ay and 3az was then achieved
[*] Prof E. Nakamura, Y Yu, S . Mori
Department of Chemistry, The University of Tokyo
Bunkyo-ku, Tokyo 113 (Japan)
Fax: Int. code +(3)5800-6889
e-mail : nakarnurai? chem.s,u-tokyo.ac.jp
Dr. S . Yamago
Department of Synthetic Chemistry and 3iological Chemistry
Kyoto University (Japan)
['*I This work was supported by the Ministry of Education, Science, Sports, and
Culture and the Sumitomo Foundation (financial support and a Monbusho
scholarship to Y Y ) .We thank the Institute for Molecular Science, Japan, for
computational time. S . M. thanks the JSPS for a predoctoral fellowship.
374
Q VCH VerlagsgesellschuftmbH, 0-69451 Weinherm, 1997
1
2
A'
a
a; R' = C,H,
b; R' = H
R'
5
x; R2 = CH2C(CH&CH20H
y; R2 = CH,
2;R2 = pNO&H,
with NaBH, at 0°C. The same procedure was applied to the
unsubstituted cyclopropene l b to produce the acrylate derivatives 3by and 3bz in 70-80 % yield. Photolysis of the ( Z ) methyl
ester 2ay affords the ( E )isomer 4ay (28 % yield, 60 % recovery
of 2ay), which was reduced to provide the (E)-olefinic mercury
hydride 5ay in 78% yield.
The hydridomercury acrylate derivatives 3 and 5 are stable,
colorless solids. The stability increases from the methyl ester 3ay
(half-life t , / , = 34 h at 75 "C in C6D6)to thep-nitrophenyl ester
3az ( t l i 2 =74 h at 75°C in C,D,). Thep-nitrophenyl esters 3az
and 3bz remain unchanged for many weeks as a solid at 4 "C and
in benzene solution at 25 "C. The hydride 32 decomposes with
s-' at 75 "C in dea first-order rate constant of k = 2.6 x
gassed C,D6. The corresponding deuteride 3D-az is much
longer lived ( k = 9 . 6 lo-'
~
s-', t l i z = 201 h at 75°C in degassed C6D,) .L6] The remarkable stability of 3 is in sharp contrast to the instability of previously known RHgH compounds
(tliz = 100 min at 20°C for CH,HgH in
Some
spectral properties correlate with the stability of the compounds. The IR stretching frequency (KBr) of the Hg-H bond
increases from the methyl ester 3ay (1969 cm- ') to the p-nitrophenyl ester 3az (1983 cm-I). The Hg-H coupling constant in
the NMR experiment increases from 3118.3Hz for 3ay to
3218.0 Hz for 3az. The substituent R' (Et, H) does not significantly affect the stability of the hydrides. The 2 and E isomers
of the methyl esters 3ay and 5ay are of comparable stability
(tliz = 34 h and 23 h, respectively, at 75 "C in degassed C,D,).
This indicates that coordinative interaction between the ester
and the mercury atom is not very important for the stability of
the hydrides. In line with this observation is the fact that reduction of 2-(ethoxycarbonyl)ethylmercury(11) chloride['] with
NaBH, does not give the corresponding isolable mercury hydride, which would be a saturated analog of 3ay.
Thermolysis of 3ay and 3az nearly exclusively produces the
divinylmercury compound 8 (90- 100 % yield) and metallic mercury. Only traces of the normal reductive elimination products
11 (Scheme 3 ) could be found. Formation of 8 suggests intervention by the dimer 7,hence implying that 6 is long-lived enough
to be chemically trapped. Indeed, when 3ay was treated with the
halogenating agents NCS, Cl,CBr, CCl,, and tBuBr (listed in
order of decreasing halogen donating ability[']), the halogenated products 9ay (X = C1, Br) were formed in 90,76,23, and 6 YO
yield, respectively. Addition of hydroquinone (11 mol YO)to the
reaction mixture resulted in a decrease in the rate of halogenation with C1,CBr and formation of the dimer 8ay (Say: 44%;
9ay: 51 YOyield). Use of an inferior radical acceptor, such as
0570-0833/97/3604-0374$ 1S.OO-t .25/0
Angen. Chem. Int. Ed. Engl. 1997, 36, No. 4
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