The Sakurai reaction of 4-acetoxycyclopentenone - Synthesis of trans-3- allyl-4-vinylcyclop entanone

Article abstract of DOI:10.1055/s-1999-3100

The Sakurai reaction of 4-acetoxycyclopentenone 1a leads to the aldol 2 and the bicyclic product 3. Retroaldol reaction leads to 4- allylcyclopentenone 7, from which the title compound 9 was prepared in 28% overall yield. Further transformations of 3 are reported.

Full text of DOI:10.1055/s-1999-3100

LETTER
881
The Sakurai Reaction of 4-Acetoxycyclopentenone – Synthesis of trans-3-Allyl-
4-vinylcyclopentanone
V. Helbling, M. K. Eberle, R. Keese*
Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
Fax +41(31)6313423; E-mail: reinhart.keese@ioc.unibe.ch
Received 29 January 1999
Albert Eschenmoser for his visions and perspectives in Science
Addition of allyltrimethylsilane to a mixture of 1a and ti-
Abstract: The Sakurai reaction of 4-acetoxycyclopentenone 1a
tanium tetrachloride in dichloromethane at -78°C gave 2
and 3 in 69% and 11% yield, respectively (Scheme 1). In
leads to the aldol 2 and the bicyclic product 3. Retroaldol reaction
leads to 4-allylcyclopentenone 7, from which the title compound 9
addition, small amounts of 1b and of the dimer of cylco-
pentadienone have been detected. When the reaction was
run with a large excess of allyltrimethylsilane for 2d small
amounts of 4 (8%) and 5 (5%) were isolated as well. Nei-
ther the expected 3-allyl-4-acetoxy-cyclopentane 6 nor
the elimination product 7 were found.
was prepared in 28% overall yield. Further transformations of 3 are
reported.
Key words: allyltrimethylsilane, 4-acetoxycyclopentenone, aldol
products, 5-trimethylsilyl-bicyclo[3.3.0]octan-1-one, stereoelec-
tronic control
Surprisingly, the enolate intermediate of the Sakurai reac-
tion, formed by normal allylation reacted with a second
molecule of 1a leading after elimination of acetic acid to
the aldol product 2 obtained as a mixture of stereoisomers.
A single isomer of unknown configuration was isolated by
HPLC. The product of the annulation reaction and elimi-
nation of the acetoxy group, 3 is obtained as a single ste-
reoisomer (see below). The structure of 2 suggested that
the 4-allylcyclopent-2-enone 7 might be obtained by a ret-
roaldol reaction. Treatment of 2 with a variety of bases did
not lead to the desired cleavage. However, reaction of 2
with ammonia at r.t. gave the desired 7 accompanied by 8
in 59% and 17% yield, respectively. The subsequent Cu(I)
induced 1,4-addition of vinyl magnesiumbromide to 7
gave the target compound 9 in 69% yield, with an overall
yield of 28% for the transformation 1a → 9. Since the
NMR spectra of 9 did not give a conclusive answer about
the stereochemistry, the carbonyl group was reduced to
the two stereoisomeric hydroxy compounds 10 and 11
(Scheme 2). The H atoms in both stereoisomers have been
assigned from their H-H- and C-H COSY NMR spectra.
In the course of our continuing efforts to prepare
polyquinanes and to study their properties, we visualized
trans-1-allyl-2-vinylcyclopentane with a functionality in
the non adjacent position like 9 as an attractive intermedi-
ate.1-5 To prepare this target compound in a few steps we
considered the readily available 4-acetoxycyclopent-2-
enone (1a) as the key synthon.6-7 Allylation of enones by
TiCl4 induced reaction with allyltrialkylsilanes according
to Sakurai is well established and should lead in the case
of 1a to the intermediate 6, which after base induced elim-
ination of the β-acetoxy group is ready for stereoselective
Cu(I) promoted trans-addition of a vinyl anion.8 Most re-
cently Robertson has reported an intriguing alternative to
TiCl4.9 Here we report our surprising results of the TiCl4
induced reaction of 4-acetoxycyclopent-2-enone (1a)
with allyl-trimethylsilane leading preferentially to the al-
dol product 2 accompanied by the bicyclic compound 3.
The successful preparation of trans-3-allyl-4-vinylcyclo-
pentanone 9 from 2 and further transformations of 3 are
described.
Scheme 1
Scheme 2
Synlett 1999, S1, 881–884 ISSN 0936-5214 © Thieme Stuttgart · New York

882
V. Helbling et al.
LETTER
Comparison of the chemical shifts of the bridgehead pro- treated with titanium tetrachloride and allyltrimethylsi-
1
tons in the H NMR spectra and NOE interactions re- lane the bi- and tricyclic compounds 4 and 5 were formed
vealed the trans configuration of the allyl and the adjacent in 53% and 24% yield respectively. The stereochemistry
vinyl group: In 10 as well as in 11 the tertiary H atoms of the triquinane 5 is based on its C2 symmetry compatible
trans to the hydroxy group (10: Ha, 11: Hb) showed a NOE with the 2 signals in the GC on a chiral GC-column and
interaction with the H atom adjacent to the hydroxy group. the 7 13C NMR signals observed.
The bicyclic compound 3 is formed as a minor product in
the stereoselective reaction of 1a with allyltrimethylsi-
lane. The exo position of the trimethylsilyl substituent is
suggested by the absence of a NOE signal between the ad-
jacent H atom and the bridgehead H atoms as well as by
the close analogy to the reaction of cyclopentenone 12
Taking into account the results and mechanistic interpre-
tations of Knölker, Danheiser and Meyers, the highly ste-
reoselective processes by which 3, 14a and others are
formed, can be described by a stereoelectronically con-
trolled attack of the allylsilane in the 3-position of the ac-
tivated enone in a synplanar or an antiplanar conformation
(Scheme 4, shown only for an antiplanar conformation of
with tris(isopropyl)-allylsilane which gives 14b as the
major product.10 Although 12 reacts with allyltrimethylsi-
the enone).9, 14-15 A priori the allylsilane can adopt an 'en-
lane to 3-allylcyclopentanone 13 in good yield, we sur-
do'- or an 'exo'-orientation. Whereas allylation could pro-
ceed by nucleophilic attack at the silyl group (process a)
from the endo- as well as from exo arrangement, an endo
orientation of the allyltrialkylsilane is required for the ob-
mised that the bicyclic product 14a with an exo-TMS
substituent might be present as well (Scheme 3). If so, it
would support the exo configuration of the trimethylsilyl
group in analogy to the tris(isopropylsilyl) group in 14b.
served exclusive formation of the cyclopentane ring with
the carbonyl and silyl group trans to each other (14a).16
This ring formation becomes the dominant process (pro-
cess b) by use of bulky alkylsubstituents at Si.
Scheme 3
Scheme 4
Cyclopentenone (12) was treated with allyltrimethylsilane
The Sakurai reaction has proven to be a valuable addition
and TiCl4 according to the known procedures.8, 11-12 After
to the arsenal of reliable and efficient synthetic methods.8
workup the crude product was purified not by distillation
Specifically the cycloalkenones 12 and 16 (n = 2, 3) give
upon treatment with TiCl4 and allyltrimethylsilane the 3-
but by CC, instead.13 A mixture of 13 (GC-yield 20%) and
14a (GC-yield 7%) was eluted first. Then, the crystalline
allylcycloalkanones in high yield (13: 70 %8b; 17 n = 2: 80
aldol product 15 was isolated in 8% yield. The formation
%8b, 17 n = 3: 84 %18). Depending on the structure of the
of 15 is most likely due to the direct reaction of the
enone and the bulk of the trialkylsilyl group allylation is
titaniumenolate, produced by allylation of 12, with bicy-
clic ketone 14a.
accompanied by a competing annulation reaction .10,14-15
This latter reaction becomes the dominant path when the
The X-ray structure analysis of 15 clearly reveals an exo- trimethylsilyl substituent of the allylsilane is replaced by
configuration of the trimethylsilyl group. Under con- bulkier trialkylsilyl groups. For the reaction of cyclopen-
trolled GC conditions 15 underwent a retro aldol reaction tenone 12 with allyltrimethylsilane our more detailed in-
giving the bicyclic ketone 14a as well as 3-allylcyclopen- vestigation has revealed a more complex reactivity
tanone 13. Hydrogenation of 3 led to a product, which ac- pattern. Whether this is due to the formation of binary or
cording to its 1H NMR sprectrum was identical with that higher Ti(IV)complexes in the course of the reaction is an
of 14a.
unsolved question.19 Nevertheless, the high yield as well
as the control of the chemo- and stereoselectivity ob-
With the bicyclic compound 3 at hand, the further reaction
with allyltrimethylsilane was of interest. When 3 was
Synlett 1999, S1, 881–884 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Synthesis of trans-3-Allyl-4-vinylcyclopentanone
883
served in the reaction of enones with allyltrialkylsilanes is 2.05(dd, J=18.7, 2.2, 1H). 13C-NMR: 214.1(s), 167.6(d),
the basis for its synthetic importance. 134.9(d), 134.2(d), 117.5(t), 40.8(d), 40.3(t), 38.5(t).
In contrast to this high selectivity 4-acetoxycyclopent-2- Trans-3-allyl-4-vinyl-cyclopentanone (9): To a mixture,
enone 1a reacts preferentially to 2 and the annulation prepared from 7.0 ml vinyl-MgBr in THF(15%, 7.00
product 3 rather than to the expected Sakurai product 6 or mmol) and 0.119 g CuBr x (CH3)2S in 18 ml THF at
7. The aldol compound 2 can be cleaved upon treatment –70°C was slowly added 0.710g (5.8mmol) 7 in 10ml
with a weak base to give the desired 4-allylcyclopent-2- THF. After stirring for 1.5 h at -78oC the reaction mixture
enone 7 directly in good yield, from which 3-allyl-4-vi- was worked up, extracted with ether (3x) and the residue
nylcyclopentanone 9 can be readily prepared.
purified by FC with hexane-ether = 1:1 to give 0.60 mg
(69%) 9: Rf (hexane-ether = 1:1): 0.73. IR: 3010(m),
1740(vs), 920(s). H NMR: 5.75(m, 2H), 5.08(m, 4H),
Experimental details.20
1
3-Allyl–2-[1-hydroxy-4-acetoxycyclopent-2-enyl]-cyclo-
pent-4-enone (2). To a solution of 3.40g (24.0 mmol) 1a7
in 140ml CH2Cl2 was injected 4.54g (24.0 mmol) freshly
distilled TiCl4 at -78oC under vigourous stirring. After
stirring for 20 min a cooled (-78oC ) solution of 6.40g
(48.0 mmol) allyltrimethylsilane in 80ml CH2Cl2 was
slowly added during 1h. The reaction mixture was
warmed to -25oC and stirred for 20h. Hydrolysis with an
ice cold solution of NaHCO3 and extraction with CH2Cl2
(3x) gave after work up and CC with hexane-ether (1:1)
4.35g (69%) 2 and 0.52g (11%) 3. In addition traces of 1b
and dicyclopentadienone were isolated. A pure isomer of
2 was isolated by HPLC: Rf (hexane-ether = 1:1): 0.17.
IR: 3600 (w), 1730(ws), 1690(vs), 1370(s), 1245(vs),
1020(s). MS: 262(M+, 3), 220(12), 205(27), 202(19),
184(5), 174(5), 171(6), 161(10), 141(10), 123(22),
122(100), 121(20), 107(34), 94(40), 86(73), 84(82),
81(59), 79(29), 53(12), 49(15), 47(21), 43(29), 18(10). 1H
NMR: 7.68(dd, J=5.5, 2.3, 1H), 6.25(dd, J=5.5, 1.8, 1H),
6.05-5.97 (m, 2H), 5.80-5.62 (m, 1H), 5.54-5.46(m, 1H),
5.17-5.04 (m, 2H), 4.60(s, 1H), 2.10-2.50(m, 5H), 2.05(s,
3H), 1.84 (dd, J =15.1, 3.3, 1H). 13C-NMR: 217(s),
170.8(s), 168.4(d), 139.6(d), 134.2(d), 134.1(d), 132.4(d),
118.4(t), 84.8(s), 77.4(d), 56.3(d), 44.3(d), 42.0(t),
37.9(t), 21.1(q). HR-MS: 262.1205 (calc. C15H18O4
262.1205).
2.56-2.39(m, Ha + 3H), 2.19-1.85(m, 3H + Hb). 13C NMR:
217.1(s), 139.3(d), 135.8(d), 116.7(t), 116.1(t), 46.5(d),
45.1(t), 44.0(t), 42.0(d), 37.0(t). FAB-MS: 150.0(M+, 12),
149.0 (100). GC-MS: 150(M+, 44), 135(30), 132(24),
108(14), 92(10), 81(14), 80(17), 79(15), 68(23), 67(37),
54(100), 41(32), 39(37), 27(22). Anal. calc. for C10H14O:
C 79.94, H 9.40; found: C 79.65, H 9.38.
(rel-1R,3R,4S)-3-Allyl-4-vinyl-cyclopentanol (10) and
(rel-1S,3R,4S)-3-Allyl-4-vinyl-cyclopentanol (11): A so-
lution of 0.56 g (3.7mmol) 9 in 10ml methanol was slowly
added to 0.156 g (4.1mmol) NaBH4 in 20ml methanol. Af-
ter 15 min 5ml dist. water was added and the reaction mix-
ture worked up. HPLC gave 0.27 g (48%) 10 and 0.242 g
(43%) 11. 10: Rf (hexane-ether = 1:1) : 0.28; k’ (HPLC):
1
7.6. IR: 3615(s), 3480(s), 1010(vs), 915(vs). H NMR:
5.90-5.75(m, 1H), 5.75-5.60(m, 1H), 5.10-4.9(m, 4H),
4.40-4.30(m, 1H), 2.60-2.50(m, Ha), 2.50-2.40(m, 1H),
2.40-2.30(m, 1H), 2.15-2.05(m, 1H), 2.00-1.90(ddt, 1H),
1.85-1.75(m, 1H), 1.75-1.70(m, Hb), 1.60(s, 1H), 1.45-
1.35 (m, 1H). 13C NMR: 141.5(d), 137.4(d), 115.5(t),
114.5(t), 72.2(d), 47.8(d), 44.0(d), 42.8(t), 41.5(t), 38.3(t).
11: Rf 0.25 (hexane-ether = 1:1); k’(HPLC, hexane-
ethylacetate = 20:1): 8.1. IR: 3610(m), 3450(s), 1330(m),
1070(m), 1010(vs), 915(vs). 1H-NMR: 5.85-5.70(m, 2H),
5.05-4.90(m, 4H), 4.35-4.25(m, 1H), 2.40- 2.20(m, 2H),
2.15-2.00(m, Ha), 2.00-1.90(m, Hb), 1.90-1.78(m, 2H),
1.60-1.40(m, 3H).13C-NMR: 142.1(d), 137.3(d), 115.5(t),
114.2(t), 72.2(d), 49.0(d), 42.9(d), 42.6(t), 41.7(t), 37.7(t).
MS (mixture of 10 and 11): 152(M+, 5), 151([M-1]+, 18),
137(17), 135(20), 124(42), 111(46), 110(39), 109(46),
91(64), 83(100). HR-MS: calc. for C10H16O 152.120115,
found 152.11850.
3: Rf (hexane-ether = 1:1): 0.73. M.p: 24-28oC. IR:
1705(vs), 1250(s). MS: 194(M+, 100), 79(56), 105(10),
153(50), 75(43), 73(80), 47(17), 28(22), 18(43). 1H NMR:
7.48 (dd, J1=5.5, J2=2.8, 1H), 6.15 (dd, J1=5.5, J2=1.8,
1H), 3.40-3.33 (m, 1H), 2.66 dd, J1=9.7, J2=5.4, 1H), 1.91
(dd, J=12.9, 5.9, 1H), 1.62 (ddt, J=12.9, 5.9, 1.3, 1H),
13
1.55-1.43 (m, 2H), 0.72-0.61 (m, 1H), 0.00 (s, 9H). C-
4-exo-Allyl-7-exo-trimethylsilyl-bicyclo[3.3.0]octan-2-
one (4) and rel-(1R,3R,5S,7R,8R,10S)-5,10-bis-trimethyl-
silyl-tricyclo[6.3.0.03,7]-undecan-2-one (5): A solution of
0.34 g (1.75 mmol) 3 in 5ml CH2Cl2 was added dropwise
to a solution of 0.365g (1.93 mmol) TiCl4 in 5ml CH2Cl2
at -78oC. After slow addition of 0.30g (2.63 mmol) allylt-
rimethylsilane in 1ml CH2Cl2 the reaction mixture was
stirred at -78oC , warmed to -20oC and stirred for 20h.
Work up and CC with hexane-AcOEt = 20:1 gave 0.180
g(53%) 4 and 0.067 g (24%) 5. 4: Rf (hexane- AcOEt =
20:1): 0.65. IR: 1720(s), 1250(vs), 1150(s), 1100(vs),
910(s), 895(s), 850(vs). 1H NMR: 6.00-5.85(m, 1H), 5.25-
5.15(m, 1H), 2.90-2.80(m, 1H), 2.70-2.60(m, 1H), 2.55-
2.35(m, 3H), 2.30-2.10(m, 2H), 2.00-1.85(m, 1H), 1.85-
1.75(m, 1H), 1.70-1.55(m, 2H), 1.05-0.85(m, 1H), 0.05(s,
NMR: 214.0(s), 167.6(d), 135.1(d), 50.7(d), 47.7(d),
32.2(t), 31.2(t), 22.4(d), -3.0(q). HR-MS: 194.1309 (calc.
for C11H18OSi 194.1307).
4-Allylcyclopent-2-enone (7): After addition of 2.86g
(10.9 mmol) 2 in 10ml CH3OH to a mixture of 80ml aque-
ous NH3 (25%) and 100ml CH3OH in 15 min the solution
was refluxed for ~ 1.5 h. The organic phase obtained by
dilution of the reaction mixture with ice cold aqueous
NaHCO3 and extraction with hexane (3x) was treated with
2N HCl (3x). CC with hexane-ether (1:1) gave 0.785g
(59%) 7 and 0.226g (17%) 821. 7: Rf (hexane-ether = 1:1):
0.38. IR: 1710(vs). 1H NMR: 7.65(dd, J1=5.6, J2=2.6, 1H),
6.19(dd, J1=5.6, J2=1.9, 1H), 5.78(m, 1H), 5.13(m, 2H),
3.05(m, 1H), 2.53(dd, J=18.7, 6.2, 1H), 2.27(m, 2H),
Synlett 1999, S1, 881–884 ISSN 0936-5214 © Thieme Stuttgart · New York

884
V. Helbling et al.
LETTER
9H). 13C NMR: 221.9(s), 136.5(d), 116.4(t), 53.5(d),
47.6(d), 45.8(t), 40.6(d), 40.2(t), 35.4(t), 32.3(t), 25.4(d),
-3.0(q). MS: 236(M+, 25), 221(12), 196(36), 195(100),
153(23), 123(27), 105(11), 86(45), 84(49), 75(15),
73(46), 47(12). HR-MS: 236.1592 (calc. for for C16H24OS
236.1596). 5: Rf (hexane- AcOEt = 20:1): 0.79. M.p.: 80-
82°C. IR: 1725(vs), 1250(vs), 920(s), 850(vs). MS:
308(M+, 8), 267(38), 235(15), 195(75), 194(22), 193(23),
179(23), 153(15), 105(15), 75(28), 73(100), 32(39),
28(96), 18(47). 1H-NMR: 2.70-2.60(m, 2H), 2.40-2.30(m,
2H), 2.05-1.95(m, 2H),1.75-1.50(m, 6H), 0.90-0.80(m,
2H). 13C-NMR: 228.3(s), 55.7(d), 48.8(d), 37.9(t), 33.9(t),
25.7(d), -3.0(q). HR-MS: 308.1996 (calc.C17H32OSi2
308.1992).
(3) M. Thommen, A.L. Veretenov, R. Guidetti-Grept, R. Keese,
Helv. 1996, 79, 461-476.
(4) R. Aebi, W. Luef, R. Keese, J.Org.Chem. 1994, 59, 1199-
1204.
(5) W. Luef, R. Keese in B. Halton, ed. Advances in Strain in
Organic Chemistry, JAI: Greenwich, Ct., Vol. 3, 1993, 229-
267.
(6) a) V. Osterthun, E. Winterfeldt, Chem. Ber. 1977, 110, 146-
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b) M. Harre, P. Raddatz, R. Walenta, E. Winterfeldt, Angew.
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62, 86-94; Coll. Vol 7, 443-446.
5-Trimethylsilyl-bicyclo[3,3,0] octan-1-one (14a).
(9) N. Kuhnert, J. Peverley, J. Robertson, Tetrahedron Lett.,
1998, 39, 3215-3216.
a) via preparative GC: GC of 15 at 120 -130 °C (20% XF
1150)) gave 13 (tR = 7.1 min) and 14a (tR = 15.78 min).
14a: 1H NMR: 2.80-2.95 (m, 1H) 2.55-2.65 (m, 1H) 2.10-
2.40 m, 3H) 1.95 - 2.05 (ddd, 1H) 1.40 - 1.65 (m, 4H) 0.75
- 0.92 (m, 1H) -0.03 (s, 9H). 13C NMR: 223.71 (s) 53.03
(d) 41.26 (d) 39.60 (t) 36.26 (t) 32.63 (t), 27.51 (t) 25.32
(d) -2.98 (q). MS: 196(M+,10) 181(12), 155(81), 156(19),
75(40), 73(100) 54(25). HR-MS: calcd. for C11H20OSi:
196.128344; found 196.127610.
(10) a) H.-J. Knölker, N. Foitzik, H. Goesmann, R. Graf, J.-B. Pan-
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4120.
b) via hydrogenation: A solution of 3 (98 mg, 0.5 mmol)
in ether (10 mL) was hydrogenated in the presence of 5%
Pd/C (50 mg). The crude product (100 mg) was distilled
in a Kugelrohr bp 110 °C (0.4 mm) purified by preparative
GC. All spectral data (MS, 1H NMR, 13C NMR) identical
with 14a obtained from 15 by aldol cleavage.
(13) M. K. Eberle, H. Stoeckli-Evans, R. Keese, manuscript in pre-
paration.
(14) R. L. Danheiser, B. R. Dixon, R. W. Gleason, J. Org. Chem.
1992, 57, 6094-6097.
(15) M. D. Groaning, G. P. Brengel, A. I. Meyers, J. Org. Chem.
1998, 63, 5517-5522.
(16) Small amounts of cis-products have been detected in a few ca-
ses:
[10d][14]. In [17] the stereochemistry of the ring closing pro-
duct has not been reported.
Acknowledgement
This work has been generously supported by the Swiss National
Science Foundation (Project No. 20-43565.95 and 2000-
050731.97). We thank Bayer AG, Leverkusen for a generous gift of
cyclopentenone, Prof. Knölker for an instructive discussion and
Prof. P. Bigler for NMR- measurements.
(17) J. Ipaktschi, A. Heydari, Angew. Chem. 1992, 104, 335-336;
Angew. Chem. Int. Ed. Engl. 1992, 31, 313.
(18) H.-R. Leu, H. Schori, R. Keese, Chimia 1981, 35, 12-14.
(19) C. A. McAuliffe, N. Bricklebank in R. B. King, Ed., Encyclo-
pedia of Inorganic Chemistry, Wiley: New York, 1994, Vol.
8, 4197-4206.
(20) Z. Teng, C. Boss, R. Keese, Tetrahedron 1997, 53, 12979-
12990.
References and Notes
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1982, 60, 2965-2975.
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Article Identifier:
1437-2096,E;1999,0,S1,0881,0884,ftx,en;W04499ST.pdf
Synlett 1999, S1, 881–884 ISSN 0936-5214 © Thieme Stuttgart · New York