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Enantioselective Cycloisomerization of 1 6-Enynes Catalyzed by Chiral DiphosphaneЦPalladium Complexes.

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Chivn. So(. 1983, 105. 5939: L. Hofinann. H. Werner. J. Organonie~.Cheni.
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624: J. Nakaydma, K. Akimoto. M. Hoshino. J. P l i ~ s Org.
G. W. Kirby. A. N. Tretheway. J. Clieni. Soc. Chem. Conimrm. 1986. 1152; R.
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N. Tokitoh. N. Takeda. R. Okazdki, J. Am. Citein Soc. 1994, 116. 7907.
N. Tokitoh. N. Takeda. T. Imakubo, M. Goto. R. Okazaki. Cli~ni.LrJrr.1992.
1599; Bull. Chem. Soc. Jpn. 1995, 68, 2757.
TbtCHSe, 4 was prepared by the reaction of TbtCHN,[9] with
(C,H,),TiSe,[li~ in the presence of a catalytic amount of CuCl at room temperature. 4 was obtained as an inseparable mixture of compounds with different numbers of selenium atoms. the average number of which was determined
to be 5.1 by elemental analysis.
A. Shaver, J. M. McCall, Organomerol/ics 1984. 3. 1823.
Compound 7 gradually decomposes to TbtCHO and MesNCSe at room temperature.
S. Watanabe, T.Kawashirna, R. Okazaki. unpublished results.
The structures of l a and Ib in solution were determined by ' H ( ' H i nuclear
Overhauser effect (NOE) experiments, !he results of which were similar to
those for TbtCHS[8]. For rotational isomerization of sterically congested.
substituted benzenes, see: J. Siegel. A. Gutierrez. W. B. Schweizer. 0.Ermer. K.
Mislow. J. A m . C/i@t77.
SOC.1986, 108. 1569: J. S. Lomas, V. Bry-Capdeville. J.
Chem. SOC.Perkin T,.uns. 2 1994. 459. and references therein.
G. Erker. R. Hock, C. Kriiger. S. Werner, F. G Kllrner, U. Artschwager-Perl.
Angew Chem. 1990. 102. 1082; Angew. Chem. In!. Ed. Engl 1990. 29. 1067
M = 968.16. trtclinic, space
Crystallographic data for 3a: C,,H,,O,SeSi,W.
group Pi, (I =12.859(3). b =16.680(7), r =11.748(6),&. Y =107.67(3),
=97.32(3), ;.=95.50(3)', V=2357(1)A3. Z = 2. pcrlcd=1.364gcm-'.
LI = 34.09 c m - ' . The final cycle of full-matrix least-squares refinement was
3.000(0] and 415 variable parameters
based on 2776 observed reflections [ I i
with R (R,) = 0.054 (0.032). Further details of the crystal structure investigation may be obtained from the Director of the Cambridge Crystallographic
Data Centre. 12 Union Road. GB-Cambridge CB2 1EZ (UK), on quoting the
full journal citation.
F. H Allen, 0.
Kennard. D G. Watson. L. Bramrner. A. G . Orpen, R. Taylor.
J. Chrni. Soc. Perkm Trans. 2 1987, S1.
P. R. Brooks, J. A. Counter. R. Bishop. E. R. T. Tiekink. Acru Crcsrullogr.
Sect. C 1991. 47. 1939.
K. Okuma. K. Kojima. I. Kaneko. Y. Tsujimoto, H Ohta, Y. Yokomori, J
Climni. Soc. Perkin Trans. 1 1994. 2151.
the construction of a stereogenic center offers an economical
access to optically active five-membered cdrbo- and heterocycles, which occur abundantly in natural products. To date, only
two examples of asymmetric induction have been reported utilizing 1) optically active carboxylic acids in conjunction with
Pdor31and 2) chiral phosphanes for the double stereodifferentiation of optically active ~ubstrates.'~]
We now demonstrate that
chiral diphosphane-Pd complexes effectively catalyze this interesting cycloisomerization, furnishing 1,4-dienes in medium to
high enantioselectivities.
Although phosphane ligands reduce the rate of the cyclization, they are crucial for smooth conversion and for minimizing
side reactions. Pd complexes with (S,S)-(R,R)-TRAP ligands
4['] were found to be particularly effective for the cyclization of
l a (R = SiMe,) at room temperature [Eq. (a), Table 11. In-
' i
Ar M e
Table 1. Enantioselective cycloisomerization of 1.6-enynes l a (R
lyzed by TRAP-palladium complexes [a].
TRAP 4 (Ar)[b]
Yield [YO]
Enantioselective Cycloisomerization of
1,6-Enynes Catalyzed by Chiral
Diphosphane-Palladium Complexes
Andreas Goeke, Masaya Sawamura, Ryoichi Kuwano,
and Yoshihiko Ito"
4 b (p-CH30CbH,)
4 c (p-CIC,H,)
4d (p-FC,H,)
4 e (p-F,CC,H,)
4f (m-F,CC,H,)
4 g (3,5-(CF,)>C,Hd
4 h (2-fury])
66 If1
Product 2 a
ee ["h]
SiMe,) cata-
Config. [el
58 14
76 kl
( R)
( R )[fl
( R )[gl
The cycloisomerization of 1.6-enynes in the presence of Pd',
acetic acid, and phosphane ligands reported by Trost opened
elegant pathways to 1,3- and 1,4-dienes, which are difficult to
produce using other methods. 1,3-Dienes with exocyclic double
bonds are suitable for Diels-Alder reactions.''. 21 Of particular
interest is the formation of the Alder-ene type 1,4-diene, since
[a] Reactions were carried out in benzene at 40°C for 5 h ; la:[Pd,(dbd),]
.CHCI,:4:HOAc = 100:2.25:8.3:180, [b] (S,S)-(R,R)-configurated TRAPs were
used. [c] Yield after purification by chromatography. [d] Determined by HPLC
with Chiralcel OJ. [el Assigned based on elution behavior on chiral HPLC
analogous to that of 2e (Table 2. entry 5). [fl 25 "C for 12 h. [g] 0" C for 24 h with
2.7 equiv of acetic acid; starting material was recovered.
creasing the electron-withdrawing ability of the ligand P-aryl
substituents (4a, 4 b < 4c, 4d < 4e) resulted in higher selectivities and also higher reactivities. With 4 e cyclization occurred
even at 0 "C (76% ee, 24% yield), whereas the reaction with 4 a
did not occur at this temperature. On the other hand, ligands
4f-h did not lead to better results. For the meta-substituted
TRAPs 4 f and 4g, steric bulk is assumed to account for these
Prof. Dr. Y Ito, Dr. A. Goeke. R. Kuwano
Department of Synthetic Chemistry and Biological Chemistry
Faculty of Engineering. Kyoto University
Sakyo-ku. Kyoto 606-01 (Japan)
Fax: Int. code +(75)753-5668
Dr. M. Sawamura
Department of Chemistry, School of Science
The University of Tokyo, Hongo. Bunkyo-ku. Tokyo 113 (Japan)
results. I n addition. optically active cis-chelating phosphanes
;IS CHI RAPHOS,[61 DIOP,"] BPPFA,ls1 and PPFA['] only
led t o selectivities of 6- 15 '/o ee with conversions of 56-85 %.
Moreover. with BINAPl9l and the electron-donating EtTRAP"']
no conversion occurred even at 80 "C. Neither isomerization to
the constitutional isomer 3 nor racemization, which may be
responsible for low enantiomeric excesses of the cyclization
products, b a s observed on treatment of 2 with [Pd(PPh,),] under the reaction conditions.
The regioselective formation of 1,4-dienes 2 can be explained
by the relative ease of the b-elimination of H, over H, in the
proposed palladium(ir) intermediate B. The j-elimination of Ha,
however. is affected by steric and electronic factors and leads to
mixtures of 1.4- (2) and 1.3-dienes (3) in most cases.['* 31 When
a silylallyl
serves as the alkene component, the 1,4-dienes are formed selectively due to the kinetically enhanced acidity of the CH group z to silicon. The configuration of the double
bond in 2 was always E ( E : Z > 50: I ) , indicating that the cis-[!elimination took place out of the sterically less congested conformation. Although the reaction mechanism remains highly
speculative, we believe the trans-chelation of the TRAP ligands
to the palladium atom to be essential for the enantioselectivitydetermining step. This premise is supported by the observation
of only two doublets at 6 = 21.4 and 38.3 (J = 455 Hz) in the
31PNMR spectrum (81 MHz, C,D,, 4a as ligand, 30°C) of the
catalyst system under conditions similar to the reaction conditions described in Tdbk 1.
Results of the cycloisomerization of various 1,6-enynes (1 ai) with (S.S)-(R,R)-p-CF,C,H,-TRAP (&) are summarized in
Table 2. The replacement of one of methyl substituents of the
Table 2. Eniintiosclective cycloisomerization of 1.6-eneynes 1 catalyzed by the palladium complex oI' /I-CF,C,H,-TRAP 4e [a]
2 [el
3 If1
R (I)
SiMe, ( I a)
SiMe,Ph ( I b)
CH,SiMe, ( l c )
C,H,SiMe, ( I d )
Et ((€1-1 f)
Et ((Z)-If)
C,H,, (Ig)
CH,Ph ( 1 h)
CH,CHMe, ( l i )
8.9: I
6.8: 1
(Config.) [d]
k1] See Experimental Procedure; reaction time 24 h. [b] Determined by ' H N M R
spectroscopy [c] Determined for all compounds by HPLC using Chiralcel OJ For
the determination of the w value. 3 was removed by treatment with an excess of
i\'-phenylnialeimide in CH,CI,. [d] Assigned based on elution behavior on chiral
HPLC an;dogous 10 that of 2 ( R = Me). [el Reaction time 48 h. [fl Reaction time
20 h. [g] % - E = 96 4.
silicon atom with a phenyl group had only a limited influence on
both the reactivity and enantioselectivity (entries 1,2). The preferential formation of 1,4-dienes in substrates bearing a silylallyl
group was extinguished in substrates having a homoallyl ( I c,
entry 3) or an even more remote silyl group (1 d, entry 4), leading to some 1 .3-diene formation. Interestingly, when steric congestion was relieved by placing the silyl group on a remote
position. the enantioselectivity increased considerably, peaking
at 95% re. However. steric reasons alone cannot account for
this observation. since ee values obtained with substrates having
aikyl or phenyi substituents at the homoallylic position (1 g-i)
were lower (entries 8-10), It is important t ) note that the
product of (Z)-1f has opposite configui-atio : to that of substrate (E)-lf (entries 6, 7). Therefore, the use , )f diasteriomerically pure enynes is a prerequisite for obtainin: high enantioselectivities.
The enantioselectivity was also sensitive tog ards the sulfonamide groups. The idea of stabilizing the confoi-mation of intermediate A by the introducing bulkier sulfonamide groups was
not tenable. since the selectivities continuously decreased (data
not shown). Moreover, the reaction of an enyne carrying a
methanesulfonamide group (R = SiMe,) proceeded with very
low enantioselectivity (0 "C 11 % ee). This low selectivity may
indicate that the substituent on the sulfonamide group may be
primarily electronic.
Experimental Procedure
A solution of [Pd,(dba),] CHCI, (2.2 mg. 2.25 mol%) (db'i = dihenzylideneacetone) and p-CF,C,H,-TRAP 4e (8.6 mg, 8.1 mol "A) in toluene (0.5 mL) was stirred
under N, at 25 C for 30 min. Acetic acid was added (15mg). and after 5 min I c
(31 .0 mg, 0.093 mmol. entry 3 in Table 2) was added, and the mixture was stirred for
20 h. The solvent was evaporated in vacuo and the residue purified by preparative
thin-layer chromatography (silica gel, hexane!EtOAc 5/11 affording 2c and 3c as a
mixture (2c:3c = 3.5:1.21.1 mg. 68%). For thedetermination oftheenantioselectivity 3 e was removed by stirring the above mixture in CH,CI, ( I mL) with phenyl
maleimide (ca. 10 equiv) Purification by preparative thin-layer chromatography
(sllica gel. hexane/EtOAc 5:l) afforded pure 2 c (95% co (R). Chiralcel OJ.
[.]A3 = 31.9 ( c = 0.31 in CHCI,).
Received: September 30. 1995 [Z8437IE]
German version: A n g e ~Cherti. 1996, /(IN. 686-687
Keywords: asymmetric syntheses . complexes with phosphorus
ligands cyclizations * enynes * palladium compounds
[ I ] For a review: a) B. M. Trost in Siudres in Nuturd Produc! Chemistr~.S/ereo.\elecriiv Sjnthesis. Vo/ 8 (Ed. : Atta-ur-Rahman). Elsevier. Amsterdam. 1991,
pp 277-282: h) B. M. Trost. Arc. Chem. Re$. 1990, 23. 34-42.
[2] a) B. M . Trost, G. J. Tanoury, M. Lautens, C. Chan, D. T MacPherson. J. An?.
Chem. Sot. 1994. 116.4255-4267: b) B. M. Trost. D. L. Romero, F. Rise. ihrd.
1994, 116.4268-4278. c) B. M.Trost, M. Lautens. C. Chan. D. J. Jebaratnam.
T. Mueller. ihrd. 1991. 113. 636-644; d ) B. M. Trost. M Lautens. hid 1985,
107. 1781-1783.
[3] B M. Trost, D. C. Lee, F. Rise. Tetrahedron LL'II. 1989, 30. 651 --654.
[4] B. M. Trost. B. A. Czeskis. Tetruhedron Lert. 1994, 35. 21 I -214.
[5] (R,R)-(S,S)-TRAP = (R,R)-2.2"-Bis[(S)-I-(diarylphosphanyl)ethyl]-l .1"biferrocene a) M . Sawamura, H . Hamashima. M. Suganiira. R. Kuwano. Y.
Ito, Orgunorneta//ics. 1995. 14,4549-4558; b) M Sawamura, H Hamashima,
Y Ito. Terrahedron: Asymmetrr 1991. 2, 593-596.
[6] CHIRAPHOS = 2,3-bis(diphenylphosphanyl)butane: M Fryzuk. B. J Bosnich, J. An?. Chern. Soc 1977, 99, 6262 -6267.
[7] DIOP = 2,3-O-isopropylidene-2.3-dihydroxy-l.4-his(diphenylphosphanyl)butane: H. B. Kagan. T.-P. Dang, J. Am. Chem So<. 1972. 94. 6429.~6433.
[8] BPPFA = N.N-dimethyl-l-[1.2-bis(diphenylphosphanyl)ferrocenyl]ethylamine.
PPFA = 1 -[1 -(dimethylamino)ethy1]2-(diphenylphosphanyl)ferrocene. T. Hayashi. T. Mise. M. Fukushima. M. Kagotani. N. Nagashima. Y.
Hamada, A. Matsumoto. S. Kawakami, M Konishi. K. Kimamoto. M . Kumada. Bull. Chem. Soc. Jpn. 1980, 83. 1138 - 1 I51
[9] BINAP = 2.2'~bis(diphenylphosphanyl)-l.l'~binaphthyl. A Miyashita. A.
Yasuda. H. Takaya. K. Toriumi. T Ito. T. Souchi. R. Noyori. J Ani. Chmr Sot..
1980. 102. 7932-7934.
[lo] R. Kuwano, M. Sawamura. J. Shirai, M. Takahashi. Y. Ito. ~ ~ ~ / r - u h ~Lrrr.
1995,36. 5239-5242
[I 11 Allylsilane has already been used in an asymmetric intramolecular Heck reaction: L. F. Tietre. R Schimpf. Angeii.. Chem. 1994. 106. 1138 1139. Angrii..
Chmi. / n ! . Ed. Engl 1994. 33. 1089-1090.
[12] For the determination of both the enantiomeric excess and xbsolute configuration. the sulfonamide group was converted into a trrr-but[)xycarhonyl (Boc)
group [Li,'NH,, -78 C: (Boc),O,'Et,N]. The optical rotaiim of the resulting
carbamate ([&' = + 12.9 (c = 0.35 in CHC1.J W;IS compared %ith the rcported value for the (S)-configurated carbainate ( > 96% cc) ([I];' = - 37.3 (<
= 0 55 in CHCI,). W. Oppolzer. T. N. Birkinshaw. G. Bernardinelli. .litruhcdron Lc,f/.1990. 31. 6995-6998).
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chiral, cycloisomerization, enynes, diphosphaneцpalladium, enantioselectivity, complexes, catalyzed
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