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Kinetic Resolution of the Acrolein Dimer by Asymmetric Horner-Wadsworth-Emmons Reactions.

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@:Ti
.=Mg
= F
@ = D
o = C
Fig. 3. Structure of 3 in the crystal. Selected bond lengths [pm]: Ti-F 202.5*
(200.4-203.6). Ti-Cp:,,,,,,
204.6*. Mg-O(1.2) 206.0*, M g l - 0 1 226.8(3).
Mg2-03 235.8(4), M g l L F 4 202 6(3). Mg2-F4 201.8(3), Mg-F 190.S* (190.0190.9). The values marked with a * are average values.
bridging THF molecules in alkaline earth metal compounds are
unknown to date. Although the Mg-F distances to the Mg
bridging fluorine atom F4 (202.2 pm) correspond to the distances in the rutile lattice of MgF, (205 pm),"] the remaining
ME-F bond lengths in 3 (mean 190.5pm) are significantly
shorter. The central Ti,Mg,F,, inorganic core i s outwardly
shielded by both the Cp* groups and the coordinated T H F
molecules. Four Ti, two Mg, and twelve F atoms build a cagelike framework whose cavity has a p2-bridging fluorine atom
(Mgl -F4-Mg2) projecting into it.
With these examples, we have shown for the first time that
molecular solids can function as ligands in organometallic
chemistry. Continuing investigations are aimed at determining
how the size of the aggregates can be influenced by, for example,
changes in the ligands, the solvent, or through template effects
as well as whether corresponding oxide systems can be prepared.
Experinientul Procedure
2. A solution of I (0.72 g. 3 minol) in T H F (40 inL) wds added dropwise to a
suspension of Na (0.07 g. 3 mmol) and incrcury (10 g) in T H F (20 mL) at 0 C. The
reaction must be carried o u t under careful exclusion of Mater and oxygen. The
mixture h a s stirred for 1 2 h. filtered. and the solvent was then removed in vacuum.
Crystalline 2 (0.52 g. 65% yield) was obtained by rccrystalli7ing the green rcsidue
froin THF:hexane (20 inL'40 mL). M.p. 204 C (decamp). Thedecomposition temperature refer5 to the solrent-free compound, nhich is obtained by evacuation of 2
(lO-'mbar. 25 C. 12 h) Correct eleinental analyses. I R (Nujol): a[ciii-'] =
1497(m), 1261)(m). lOhl(s). 1027(s). 81S(s). 545(5). S07(s). 4941s). 471(s).
3 A solution of 1 (0.72 g, 3 minol) in T H F (40 mL) \ \ a s added dropwse to Mg
(0.35 p, 14 mmol) in T H F (20 mL) undei- an inert atmosphere. The magnesium h a s
first activated with HgCI, ( S mg). The mixture was stirred for 12 h a t room teinperature. filtered. and the solvent was then reino>ed in vacuum. The residue w a s
recrystallized from THF'hexane (40 mL:20 mL) which yielded 0.5 p of 3 (75%).
M p. 240 C. Correct elemental analyses t'rom the solvent-free compound
~')
1260(m). 103l(s).801(sj.
( 1 0 ~ 2 m h a r , 2 5C. l ~ l i ) . l R ( N u ~ o l ) : i j c i n =1498(mj.
519(s), MS(EI) r d ; : 873 (M-Cp*. 1.2%). 135 (Cp*, 100%).
Received: October 2. 1993 [Z6386IE]
German Version. A I Z ~ P Cheni.
I I ~ . 1994. 1/16. 577
[I] H. W. Roesky. M. Sotoodeh, M. Noltemeyer. . 4 n p v . Clieni. 1992. 104. 869;
Angeii,. Chcm. / n r . E d €nR/. 1992. 3f. 864.
[2] Crystal data for 2: C,,H,,,,,F,,Na70,Ti, + 1.2thf. M , =1X00.91, triclinic.
space group Pi.u = 1195.0(2). h =1407.7(2). c = 2670.Y(S) pm. 1 = 80.99(1),
/j=77.67(1). ~ = 7 2 . 4 6 ( 1 ) ~V=4.165(1)nm3,
.
Z = 2 . p~,,,,,=1.436gcm~'.
F(000) = 1x60. E. =71.073 pm. /i(Mok,) = 0.668 m n - ' . Thedata were collected on a Stoe-Siemens-Huber four-circle diffractometer. The intensities were
determined at - 120'C from a rapidly cooled crystal in B drop of oil 181 having
dimensions of 0.4x0.3 x0.2mni by the 2fk<,J inethod over the range
8 < 2 0 < 4 5 '. A \emiempirical absorption correction method was applied 10
the 10922 independent reflection, from the 1x706 collected. 10920 of the independent reflections and 5683 restmints were used in the refinement of 1143
parameters. Largest minimum and maximum in the final difference-Fourier
synthesis: 460 and -480 enm-'. respectively. R I ( F > 4 u ( f ) )= 0.046 and
hiR2 = 0.12X (for all data). 3: C,ZH,,Fl,Mg,O,Ti, + 4thf. .M, =1513.83.
monoclinic. space proiip P2,:m. n = 1470.9(1). / I =1679.8(2). L' =
1539.5(2)pm,/j =105.53(1) , b'= 3.6649(7)nni3,Z= 2.p,,,,, = 1 . 3 7 ? . g ~ m - ~ .
F(000) = 1600. j. =71 073 pm. p(Mokz)= 0.517 m m - ' The data were collected oii :I Stoe-Siemens-AED four-circle dift'ractometer The intensities \%ere
determined at - 120 C from il rapidly cooled crystal in a drop of oil [S]having
diinensioiis of 0.2 x0.2 x 0 . I mm by the 2 H ~ omethod over the range
8 $20 $ 50 . From the 6666 independent reflections out ofthe 8199 collected,
6663 were used together with 1416 restraints in the refinement of696 parameters. Largest minimum and maximum in the final difference-Fourier synthesis.
600 and -380enm-';. respectively. RI(F>4o(F)) = 0 048 and wR2 = 0.140
(for all data). The \ d u e s for RI and wR2 uere defined as R1 = X l \ & ) l - If,ll
[XI Pol ] : wR2 = :[Zw(F: -- Ff)'.'[Xw( I.
I ? .The btructures were solbed by
direct methods (SHELXS-90) [9]
refined by least-squares methods
(SHELXS-93) [lo). The hydrogen positions Mere refined by a riding model in
bvhich C H , group5 can rotate about their loclil threefold axes. Further details
of the crystal structure investigations may he obtained from the Director of the
Cambridge Crystallographic Data Centre. 12 Union Road. GB-Cambridge
CB2 1EZ on quoting the complete literature citation.
131 A. F. Wells. S'iriic /ui.rr/ / r r ~ ~ i . g ~ iC%onir.tri..
nic
5th ed., Oxfoi-d Uiuverstty Press.
Oxford. 1984.
[4] U. Pieper. D. Stalke. S. Vollbrecht. U. Klingebiel, Chenr.Ber. 1990. 123. 1039.
[ 5 ] S. Brooker. F. T. Edelmann. T.Kottke. H. W. Roesky. C. M. Sheldrick. D.
Stalke. K . H. Whitmire. J. C/imi. Sor Chern. Con~n7uir.1991. 144.
[h] E-Q. Liu. H. Gornitrko. D. Stalke. H. W. Roeskq. Angew. C h m 1993, 1f)J.
447: A n g n ~ ,Ch~r17 Inr 0 1 . €n,q/. 1993. 32, 441.
[7J R. D. Shannon. C. T. Prewitt.
[XI T. Kottke. D. Stalke. J. App/.
[9] G. M. Sheidrick. Acts Cr,rsio//ogr.Sect. A 1990. 46. 467.
[lo] G. M . Sheldrick. SHELXL-9.7. Giittingen. 1993.
Kinetic Resolution of the Acrolein Dimer by
Asymmetric Horner -Wadsworth-Emmons
Reactions" *
Tobias Rein," Nina Kann, Reinhard Kreuder,
Benoit Gangloff, and Oliver Reiser*
Dedicuted fo Pwft~ssorBjorn Akermnrk
on the occasion of his 60th birtizday
The Diels-Alder dimer of acrolein 1IL1is available in bulk
quantities and has great potential as a synthetic building
block['] because of its aldehyde and enolether functionality.
['I
Dr. T. Rein. DipLChein. N . Kanii
Organic Chemistry. Royal Institute of Technology
S-100 44 Stockholm (Sweden)
Telctir: Int. code + (81791 2333
Dr. 0. Reiser. R. Kreuder'-'
Institiit fur Organische Chcmie der Universitit
Tammanstrasse 2, D-37077 Giittingen (FRG)
Telefax: I n t . code + (551)399475
B. Gangloff'"
Universite de Miirseille. Marseille (France)
[ ' ] Erasmus exchange students at the Royal Institute of Technology. Stockholm.
[**I
We thank the Swedish Natural Science? Research Council, the Deutsche
Forrchungsgemeinschaft (Re 948,'l-2). Carl Tryggers Foundation for Scientific
Research. the Foundation Bcngt Lundqvists Minne. Helge Ax:son Johnsons
Foundation, and the Royal Institute of Technology for financial support. Dr.
D . Yu. Degussa AG. Germany. is acknowledged for a generous sample of
aldehyde I . Travel grants from the Erasmus program for student exchange (8.
G.) and the Bundesamt fur Ausbildungsforderung Flensburg (R. K.) are gratefull) acknouledged. We also thank Professors B. Akermark. Royal Institute OF
Technology. Stockholm. A. de Meijere. GBttingen. and P. Helqutst, University
of Notre Dame IN. USA. for their continued interest and support. and Ms.
Gurli Hammarberg Tor assistance ~ i t spectroscopic
h
analyses.
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However. 1 has not yet found wide application since it is not
available in optically pure form. As part of our ongoing studies
regarding asymmetric alkene ~ y n t h e s i s ' ~and
] the utilization of
vinyl-substituted dihydropyrans as homoaldol equivalents,[41
we have studied kinetic resolutions of racemic 1 by reactions
with chiral phosphonate reagents. In all previously reported
cases of kinetic resolution by asymmetric alkene synthesis,[51the
substrates used have been ketones. In this paper, we report that
kinetic resolutions of the aldehyde 1 can give high diastereoselectivities, and furthermore that either ( E ) - 3 or ( 2 ) - 3 can be
obtained as the main product.
2a: R = Me
1
2b: R = Et
phosphonate reagent 2d[' 'I by the same method as used for the
other reagents 2. To our delight, 2d gave high diastereoselectivity for the ( Z )product, together with useful double bond selectivity (entries 6 and 7). After chromatography, high yields of
(2)-3'"l with excellent diastereomeric purity (96-98 'In de) were
obtained.
Our assignments of the absolute configurations of the condensation products are based on the NMR analysis['41 of the
Mosher ester derivatives 4 and 5 obtained from ( E ) - 3and ( 2 ) - 3 ,
respectively, by straightforward transformations. This analysis
shows that the ( E ) and (2)
products are formed from different
enantiomers of the starting material 1. Further support for this
conclusion comes from the reaction in entry 8, in which only one
equivalent of 1 was used, also indicating that the ( E ) and (Z)
isomers are formed from different enantiomers of the starting
aldehyde. The alternative explanation of a fast racemization of
the aldehyde in the course of the reaction is unlikely since similar
( E ) / ( Z )selectivites and yields would be expected in entries 6 and
8 if racemization was faster than the condensation process.
2c:R=iPr
2d: R = CF&H,
Ph
4
Ph
Initial studies were performed by using the chiral phosphonate 2aC6] which has previously been used17] in asymmetric
alkene synthesis with ketone substrates, and has also given good
results in our studies of reactions with meso dialdehyde~.[~]
The
reaction of 1 with 2a gave high diastereoselectivities for both
( E ) - 3 and ( 2 ) - 3 (Table 1 , entry I ) , however, the ( E ) / ( Z )ratio
was only modest (39:61).[8.91To study the influence of variations in the phosphonate structure on the selectivity,["] the new
phosphonate 2b[' and the previously known reagent 2cl6I were
synthesized in the same manner as 2a. Use of 2b favored formation of the ( E )isomer (entry 2), and performing the reaction at
lower temperature (entry 3) gave a good yield of (E)-3["I with
high diastereomeric purity (88 Yn de) after chromatography. Reactions with phosphonate 2c (entries 4 and 5 ) gave even higher
( E ) / ( Z )selectivity, but the diastereoselectivities were lower."
It is known that the formation of ( 2 )alkenes in HornerWadsworth Emmons reactions is favored by using trifluoroethoxy substituents on phosphorus.[' 31 In order to enable selective preparation of the ( Z )product, we thus synthesized the new
-
Concerning the mechanistic reasons behind the observed selectivities, there are several points that need to be investigated
further before any well-founded rationalizations can be
made.["] It is not clear which reaction step is the rate-determining one for a given combination of reactants, the initial addition
of the phosphonate anion to the aldehyde or the subsequent
elimination step. Also, the analysis is complicated by the fact
that each alkene isomer might in theory have been formed from
either of two different diastereomeric /I-alkoxy anion precursors.
We are presently studying the possibility of using other types
of aldehydes as substrates in these reactions, as well as synthetic
applications. We believe that kinetic resolutions of this type
should have considerable synthetic potential.
Table 1 . Reactions of phosphonates 2 with racemic aldehyde 1 . [a]
Entry
Phosphonate
7
['C]
( E ) : ( Z )ratio,
crude [b]
Diast. ratio.
crude ( E ) [b]
Diast. ratio.
isol. ( E ) [hj
Yield. ( E )
[%] [cl
Diast. ratio,
crude ( Z ) [b]
Diast. ratio.
isol. ( Z ) [b]
Yield, ( Z )
f % ] [c]
1
2a
2b
- 78
- 78
- 100
- 78
- 100
- 78
39:61
73:27
68:32
95.5
91:9
20: 80
15:85
44.56
95:5
96:4
92:s
94:6
87:13
80:20
9614
97:3
95:5
20
70
91.9
82: 18
90:10
72: 28
86: 14
98:2
99:l
92: 8
91.9
81:19
90: 10
69:31
88: 12
98.2
99:l
92:X
55
24
29
3
8
77
2
3
4
5
6
7
8 [dl
2b
2c
2c
2d
2d
2d
-100
- 78
92:s
93:7
84:16
79~21
96 4
96:4
95:5
68
89
81
20
14
43
81
52
[a] General conditions: 2.1-3 equiv of 1, 1.1 equiv of phosphonate. 1.0equiv of potassium hexamethyl disilazide (KHMDS). 5 equiv of [18]crown-6. 0.01 0 . 0 2 ~in THF.
[b] Determined by 'H N M R spectroscopy a t 400 MHz (integrals of olefin protons). For entries 2 and 7. the diastereomeric ratios were confirmed by HPLC analysis (Chirake1
OD column). [c] Isolated yields, after chromatography ( 2 9 5 % pure by N M R and TLC). [d] Only 1.0 equivalent of 1 was used.
Aiixrki.
Chow. In!. E d Enxi. 1994. 33, N o . 5
VCH V~rlu~sge.sel1schafi
mhH. D-69451 Weinl~rim,1994
0570-0X33:94;0505-0557 8 10.00 + .25:0
551
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E.~-p-per.irnmtci/
Pmcedule
Toa solulionofthe phosphonatereagcnt Z(1.1 cquiv, 0.01-0.02ni)and [18]crown-6
( 5 equiv) in T H F at - 78 C under argon w a s added 1 .O equiv of KN(SiMe,), (0.5 M
in toluene). After 30 min. the resulting solutionYurry was added by cannula 10 a
precooled ( - 78 o r - 100 C ) solution of 1 (2.1 - 3.0 equiv) in THF. The reaction
miyture was ctirrcd for 1-4 h at -78 or - 100 C and then quenched r i t h 1 M acetic
acid in McOH followed b) pH 7 phosphate buffer. Extractive workup (ethyl acetate). drying (MgSO,). and concentration gave the crude condensation product
which as pui-ified by flash chromatography on silica gel by using 2 % EtOAc in
hexaiies. Selected ' H N M R data (400 MHr. CDCI,): ( E ) - 3 :6 = 6.57 (dd. J = 15.8.
4.4 Hz. 1 H. CH=CHC(O), major diastereomer). 6.37 (dd. J , = 5 Hz, J1 not measurable (overlapping signals). l H. CH=CHC(O), minoi- diastereomerj. 6.35 (dt.
J = 6 . 2 , 1 . 9 H r . I H ) . 5.50(dd. J = 1 5 . 7 . 1.XHr. I H ) . 4 . 8 4 ( t d . J = 1 0 . 7 . 4 . 4 H r .
1 H ) . 4.70 4.66 (m. 1 HI. 4.40-4.34 (m. 1 H ) : [ Z ) - 3 :6 = 6.33 (dd. J = 6.2. 1.7 Hr.
1 H). 6.11 (dd. .I = 1 1 7. 7.3 Hz. 1 H ) , 5.22 (tm. .I = 8.1 H z 1 H ) , 5.16 (dd. J = 1 1 .
2 Hr. 1 H. CH=CffC(O). minor diastereomer). 5.09 (dd. J = 11.X. 2 0 H/, 1 H.
CH=C/fC(O). major diastereomer). 4 78 (td, J = 10.7,4.4 HL. 1 H). 4.73 4.68 (m.
1H).
Received: Septeinber 17. 1993 [26363 IE]
German version: Airgmr. C/irvii. 1994. 106. 597
[I] R. W. Fourie. G. H. Riever in r i m h i n (Ed.: C . W. Smirh). Wiley. New York.
1962. pp 181-210.
[2] A. C. Oehlschlager, S M . Singh. Crm. J ('hem 1988. 66. 209 213. and refcrences therein.
[3] Y . Kann, T. Rein. .I. Orx. C%cnz. 1993. 58. 3802-3804.
141 S. Hillers. A. Nikliius. 0 . Reiser, J Org. C/iwr. 1993. 58. 3169-3171
[5] 21) S. Muaierowicz. A. Wr6bIewski, H. Krawczyk. liwalidron Lrrr. 1975.437440; b) S. Hancssian. S. Beandoin, h i d . 1992,33.7655-7658; c) C. R. Johnson,
N. A. Meanwell. J Am. Chrm. Soc. 1981. 103. 7667- 7669: d ) C. R . Johnson.
R. C. Elliott. N. A. Meanwell. Tr.truhci/ron Le.ir. 1982. 23, 5005 5008.
[6] S. Hatakeyama, K . Satoh. K. Sakurai. S. Takano. f i ~ r u h ~ d r oLcrr.
n 1987. 28.
2713-2716.
[7] a ) ti.-J. Gais. C i Schmiedl. W. A Ball. 1. Bund. G. Hellniann. 1. Erdelmeier.
Tr.rru/icr/ronLert. 1988, 29, 1773-1774; b) H . Rehwinkel. J. Skupsch. H. Vorbriiggen. ;bid 1988. 2Y, 1775-1776.
[8] Since the aldehyde I is quite sensitive touards decomposition, a slight excess
(2.1 3 cquivalcnts) was used. We have not determined the w o f remaining
unreacted aldehyde in any case.
(91 Only the major diastereomers of ( E ) - 3 and (%)-3[i.e. ( R . E ) - 3 and (S.Zj-3,
respectively] have been illustrated. The ( E ) : ( . Z ) ratio for the crude product
refers to the total amounts of(E)and ( Z )products. Strictly speaking. all four
isomeric products are diastereomers; for clarity. however. we have only given
diaatereomeric ratios between products with the same alkene geometry [that is
the comparison of (R.Ej-3 with (S.E)-3and of ( S . Z ) - 3 with ( R , Z ) - 3 ]
[lo] For recent revieHs covering the Horner-Wadsworth-Emmons reaction, including mechanistic aspects. see: a ) 9 . E. Maryanoff. A. B. Reitr. Chrm RPY.
1989. RY. 863 927: b) S. E. Kelly in Conipre/iensiw Orgunic Synrh
(Eds: 9. M. Trost. I . Fleming). Pergamon Press. Oxford. 1991. pp 761 773.
[ I l l Spectroscopic and analytical data ( ' H and 13C NMR. IR. MS. elemental
analysis) in accordance with the structure were obtained for this compound.
1121 An initial attempt to increase the f E ) selectivity further by using phosphonate
Zb in combination with n-butyllithium as base. instead of potassium hexarnethbl disilazide ( K H M DS);[IX]crown-6. gave a much lower diastereomeric
ratio for the / E l product.
[I31 W. C. Still. C. Gennari. Tr~rruh~dron
Lrtr 1983. 24. 4405 -4408
[I41 a ) J. A . Dale. H. S. Mosher. J. h i . C/irm.SOC.1973. Y5, 512 519; b) 1. Ohtani.
T Kusumi. Y. Kashman, H. Kakisawa. ihid. 1991. 113. 4092 -4096 and references Llierein.
leads to trimethylenemethane.ri3 To explore the potential of
this unusual C-C bond cleavage. we have subjected cyclopropane 1 to the same conditions. This molecule does not absorb light in the UV region and has a considerable energy barrier to thermally induced ring opening.[31Nonetheless, even at
10 K a C-C bond was easily broken with this new fragmentation method.
Cyclopropane (1) is inert at 10 K with respect to irradiation
with 254 nm light in a xenon matrix. This changes drastically
when bromine is mixed into the xenon matrix (ratio
bron1ine:cyclopropane: xenon = 1 : 1.5: IOOO), and subsequently bromine atoms are generated by irradiating with light
(254 nm) from a mercury-vapor lamp. After only 30 rnin. bands
corresponding to propene (3) and allyl radical (5)["]are visible
in the IR spectrum. After 24 h irradiation, the cyclopropane is
completely consumed. Alongside the bands for 3 and 5. those
from allene ( 6 ) , propyne (9). and small amounts of acetylene
and methane can be seen in the IR spectrum.[51Interestingly.
irradiation of 1 in a xenon matrix doped with CI', Br' or I' at
wavelengths greater than 270 nm (mercury-vapor lamp with
cutoff filter) produces propene (3) exclusively. The other products are only formed if the irradiation is changed to a shorter
wavelength (254 nm) . Control experiments (dependence of the
appearance and disappearance of the relevant signals on wavelength and irradiation time) show that the first observable
product is always propene (3). The allyl radical (5) is formed
from this product by loss of a hydrogen atom. Radical 5 splits
off a second H atom in forming allene ( 6 ) ,which then isomerizes
to propyne (9, Scheme 1). A C-C bond cleavage can also occur
in 5. which leads eventually to acetylene and methane (probably
via a methyl radical).
---A
Ring Opening of Cyclopropane at 10 K**
Giinther Maier* and Stefan Senger
We recently reported the irradiation of methylenecyclopropane in a halogen-doped xenon matrix, which surprisingly
[*I Prof. G Maier. S. Senger
Institut fur Organische Chemie der Universitdt
Heinrich-Buff-Ring 58. D-35392 Giessen ( F R G )
Telefax. Int. code + (641 j702-5712
[**I Small Rings, Part XI. This work b a s supported by the Fonds der Chemischen
Industrie. Part 80: G. Maier. R. Wolf, H:O. Kalinowski. Chrm. Ber., in press.
,-H'
>320
4
~
hv, XeM'
AScheme 1
7
8
If the allyl radical (5) is generated by pyrolysis of a mixture of
allyl iodide and xenon gas at 850 "C and immediately cooled to
10 K, then the product mixture subsequently formed in the 1'doped xenon matrix by irradiation is dependent on the wavelength of light used. Irradiation at 254 nm gives, as in the presence of Br' atoms, allene ( 6 ) .propyne (9), acetylene, methane,
and, contrary to expectations. traces of propene (3) by trapping
of an H atom.
The initial step in the transformation of cyclopropane (1)
should be a C-C bond cleavage. The dissociation energy of the
C-H bond is roughly 30 kcalmol-' higher than for the C-C
bond, so formation of the cyclopropyl radical (4) is unlikely. In
spite of this, we examined the behavior of 4 in a halogen-doped
matrix. The cyclopropyl radical 416] was produced by irradiation into the long wavelength band of the allyl radical 5 at
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