Syntheses with Organoboranes. XI. Allylboration of Vinylic Epoxides with Allylic Dialkylboranes

Article abstract of DOI:10.1021/ol006641g

equation presented Allylboration of representative vinylic epoxides with allyldiethylborane (1) and (2-cyclohexenyl)dicyclohexylborane (2) affords the corresponding 1,2- and 1,4-addition products. cis-1,2-Addition is favored in the reaction of 1 with 3,4-

Full text of DOI:10.1021/ol006641g

ORGANIC
LETTERS
2000
Vol. 2, No. 24
3897-3899
Syntheses with Organoboranes. XI.
Allylboration of Vinylic Epoxides with
Allylic Dialkylboranes
Marek Zaidlewicz* and Marek P. Krzemin´ski
Faculty of Chemistry, Nicolaus Copernicus UniVersity, 87-100 Torun´, Poland
zaidleVi@chem.uni.torun.pl
Received September 24, 2000
ABSTRACT
Allylboration of representative vinylic epoxides with allyldiethylborane (1) and (2-cyclohexenyl)dicyclohexylborane (2) affords the corresponding
1,2- and 1,4-addition products. cis-1,2-Addition is favored in the reaction of 1 with 3,4-epoxycycloalkenes of six- to eight-membered rings.
3,4-Epoxycyclopentene (3a) and 5,5-dimethyl-3,4-epoxycyclopentene (3b) undergo five-membered ring opening during allylboration with 1 and
2, producing the corresponding (Z)-trienols (4a and 4b) with high stereoselectivity. 1,4-Addition of 1 and 2 to monoepoxides of 1,3-butadiene
and isoprene is favored, producing predominantly the corresponding (E)-alcohols.
Vinylic epoxides are versatile synthetic building blocks, and
their synthesis and reactions are extensively studied.1 Re-
cently, we described the kinetic resolution of vinylic epoxides
with chiral dialkylboranes of high optical purity.2 Earlier,
we showed that the reduction of these compounds with
borane and dialkylboranes proceeds with high stereoselec-
tivity affording the corresponding allylic alcohols of (Z)-
configuration.3
The addition of various organometallic reagents to vinylic
epoxides provides an access to allylic and homoallylic
alcohols.4 Thus, 1,2-addition products are favored by Grig-
nard regents,5 allylstannanes,6 and tetraallyllanthanoid
complexes.7 1,4-Addition predominates with organocopper
reagents8 and copper-catalyzed reactions of organomagne-
sium9 and organozinc compounds.10 Vinylic tellurides,11
organozinc,12 and organosilicon13 compounds have also been
used. However, mixtures of regio- and stereoisomers and
rearranged products are often obtained. Clearly, new reagents
are desirable.
The reactions of vinylic epoxides with organoboranes have
not been extensively studied. Trialkylboranes react with 3,4-
epoxy-1-butene under free radical conditions affording 1,4-
addition products.14 The addition of 1-alkenylboranes in the
presence of palladium and nickel complexes provides
(5) (a) Rose, B. C.; Taylor, S. K. J. Org. Chem. 1974, 39, 578. (b)
Bloodworth, A. J.; Curtis, R. J.; Spencer, M. D.; Tallant, N. A. Tetrahedron
1993, 49, 2729. (c) So¨derberg, B. C.; Austin, L. R.; Davis, C. A.; Nystro¨m,
J. E.; Vågberg, J. O. Tetrahedron 1994, 50, 61.
(6) Naruta, Y.; Maruyama, K. Chem. Lett. 1987, 963.
(7) Fukuzawa, S.; Sakai, S. Bull. Chem. Soc. Jpn. 1992, 65, 3308.
(8) (a) Marshall, J. A. Chem. ReV. 1989, 89, 1503. (b) Marshall, J. A.;
Crute, T. D., III; Hsi, J. D. J. Org. Chem. 1992, 57, 115. (c) Harms, A. E.;
Stille, J. R.; Taylor, S. K. Organometallics 1994, 13, 1456.
(9) (a) Lee, E. R.; Lacomy, I.; Bigler, P.; Scheffold, R. HelV. Chim. Acta
1991, 74, 146. (b) Jung, M. E.; D’Amico, D. C. J. Am. Chem. Soc. 1995,
117, 7379.
(10) (a) Lipshutz, B. H.; Woo, K.; Gross, T.; Buzard, D. J.; Tirado, R.
Synlett 1997, 477. (b) Badalassi F.; Crotti P.; Macchia F.; Pineschi M.;
Arnold A.; Feringa B. L. Tetrahedron Lett. 1998, 39, 7795.
(11) Tucci, F. C.; Chieffi, A.; Comasseto, J. V.; Marino, J. P. J. Org.
Chem. 1996, 61, 4975.
(1) (a) Trost, B. M.; McEachern, E. J.; Toste, F. D. J. Am. Chem. Soc.
1998, 120, 12702. (b) Johannes, C. W.; Visser, M. S.; Weatherhead, G. S.;
Hoveyda A. H. J. Am. Chem. Soc. 1998, 120, 8340. (c) Rychlet Elliott, M.;
Dhimane, A.-L.; Maracria, M. Tetrahedron Lett. 1998, 39, 8849. (d)
Caldwell, C. G.; Derguini, F.; Bigge, C. F.; Chen, A.-H.; Hu, S.; Wang, J.;
Sastry, L.; Nakanishi, K. J. Org. Chem. 1993, 58, 3533. (e) Chang, S.;
Heid, R. M.; Jacobsen, E. N. Tetrahedron Lett. 1994, 35, 669.
(2) Zaidlewicz, M.; Krzemin´ski, M. Tetrahedron Lett. 1996, 39, 7131.
(3) Zaidlewicz, M.; Uzarewicz, A.; Sarnowski, R. Synthesis 1979, 62.
(4) Gorzynski-Smiths, J. Synthesis 1984, 629.
(12) Eshelby, J. J.; Parsons, P. J.; Crowley, P. J. J. Chem. Soc., Perkin
Trans. 1 1996, 191.
10.1021/ol006641g CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/04/2000

mixtures of 1,2- and 1,4-addition products.15 Here, we wish
to report the allylboration of vinylic epoxides. The reactions
of allyldiethylborane (1) and (2-cyclohexenyl)dicyclohexyl-
borane (2) with representative vinylic epoxides derived from
acyclic and cyclic dienes were examined.
Allyldiethylborane was conveniently prepared in 81% yield
by transmetalation of allylaluminumsesquibromide and n-
amyl diethylborinate obtained by treatment of chlorodieth-
ylborane with 1-pentanol.16 (2-Cyclohexenyl)dicyclohexyl-
borane was synthesized by the hydroboration of 1,3-cyclo-
hexadiene with dicyclohexylborane.17
3-cyclopentenone formed by rearrangement of the starting
epoxide, was obtained.19
In tetrahydrofuran 5a was not formed but the amount of
6a increased. Allylboration of 3,4-epoxy-5,5-dimethylcyclo-
pentene20 (3b) with 1 produced also the corresponding (Z)-
trienol (4b). The reaction carried out in tetrahydrofuran was
slower compared with 3a, but the product was obtained in
good purity and yield (Table 1).
Similarly, 2 reacted with 3a to give the same type of
product, (Z)-trienol (7), in moderate yield. (Z)-Configuration
of the disubstituted double bond fixed in the ring is retained
in the product.
3,4-Epoxycyclopentene (3a) reacted readily with 1 in
diethyl ether at room temperature to give one major product
in good yield (Table 1). Surprisingly, it was not the expected
A stereoselective five-membered ring opening has also
been observed in the hydrolysis of 3a in water at pH g 7
leading to the formation of (Z)-2,4-pentadienal, in addition
to cyclopentanediols and 3-cyclopentenone.21
Table 1. Allylboration of 3a and 3b with 1 at Room
Temperature
The reactivity of 3,4-epoxycycloalkenes (8a-c) toward 1
decreases with the increasing cycloalkene ring size (Table
2). Thus, 3,4-epoxycyclohexene reacted in diethyl ether at
(17) Hydroboration of 1,3-cycloalkadienes, except 1,3-cyclopentadiene,
with dialkylboranes provides preferentially the allylic borane derivatives:
Brown, H. C.; Bhat, K. S.; Jadhav, P. K. J. Chem. Soc., Perkin Trans. 1
1991, 2633. The homoallylic borane derivative formed as a minor product
(9%) does not interfere in the allylboration reaction.
(18) (5Z)-1,5,7-Octatrien-4-ol (4a). Representative Procedure. All
operations were carried out under a nitrogen atmosphere. To a stirred
solution of 3,4-epoxy-1-cyclopentene (3a) (1.23 g, 15 mmol) in diethyl ether
(15 mL), was added allyldiethylborane (1) (1.65 g, 15 mmol) at room
temperature. After 3 h, 11B NMR analysis indicated no signal at δ 85 ppm
corresponding to 1. Ether was removed and THF (20 mL) was added. The
mixture was cooled to 0 °C and oxidized with 3 M NaOH (6 mL) and 30%
H2O2 (6 mL) for 4 h at room temperature. The organic layer was separated
and the aqueous layer was extracted with diethyl ether (3 × 10 mL). The
combined organic solutions were washed with brine and dried over
anhydrous magnesium sulfate. The product was isolated by distillation: 1.45
g, 78% yield, bp 64-66 °C/3 mmHg. GC analysis on a capillary
Supelcowax-10 column (30 m × 0.32 mm) revealed (5Z)-1,5,7-octatrien-
4-ol (4a) (90%), 1-allyl-3-cyclopenten-1-ol (6a) (6%), and cis/trans-2-allyl-
3-cyclopenten-1-ol (5a) (4%). An analytical sample of 4a was separated
by preparative GC. Anal. for C8H12O (124.18): calcd 77.38% C, 9.74%
product
compositiona (%)
time
(h)
yieldb
(%)
epoxide
solvent
4
5c
6d
3a
3a
3b
3b
Et2O
THF
Et2O
THF
3
4
24
12
90
88
73
93
4
6
12
15
3
78
80
77
81
12
4
Determined by GC analysis. b Isolated yields. c cis/trans mixture.
Identified by hydrogenation and comparison with authentic samples of cis-
and trans-2-propylcyclopentanols and 5,5-dimethyl-2-propylcyclo-pentanols,
respectively. d Identified by GC comparison with authentic samples prepared
by the reaction of allylmagnesium bromide with 3a and 3b, respectively.
a
1
1
1
H; found 77.30% C, 9.78% H. H and H × H COSY NMR (CDCl3): δ
1.65 (s, 1H, OH), 2.32 (t, J ) 6.5, 2H, CH2), 4.64 (q, J ) 8.5, 1H, HC-
OH), 5.20 (m, 4H, C(1)H2, C(8)H2), 5.45 (t, J ) 9.8, 1H, C(5)H), 5.81 (m,
1H, C(2)H), 6.08 (t, J ) 11.1, 1H, C(6)H), 6.62 (dt, J ) 16.8, 10.6, 1H,
C
(7)H). 13C NMR (CDCl3): δ 42.02, 67.14, 118.28, 119.38, 130.72, 131.77,
1,2- or 1,4-addition product but the acyclic (Z)-trienol (4a)
formed by the addition of allyl group and opening of both
the epoxide and cyclopentene rings. Its structure and (Z)-
configuration of the disubstituted internal double bond was
established by 2D 1H and 13C NMR analysis.18 Only 4% of
the 1,2-addition product 5a and 6% of 6a, derived from
133.39, 133.97. 1H × 13C HETCOR NMR (CDCl3) (correlation peaks):
2.31 (t, 2H) -41.82 (C(3)H2), 4.62 (q, 1H) -66.98 (HC(4)OH), 5.20 (m,
4H) -118.01, 119.13 (C(1)H2, C(8)H2), 5.44 (t, 1H) -133.34 (C(5)H), 5.80
(m, 1H) -133.87 (C(2)H), 6.06 (t, 1H) -130.48 (C(6)H), 6.63 (dt, 1H)
-131.67 (C(7)H). The 1H and 13C NMR spectra were recorded on a Varian
Gemini 200 instrument.
(19) For comparison, the reaction of allylmagnesium bromide with 3a
in diethyl ether at 0 °C gave trans-5a (42%), 6a (23%), and the 1,4-addition
product trans-4-allyl-2-cyclopenten-1-ol (35%).
(13) Matsukashi, H.; Asai, S.; Hirayabashi, K.; Hatanaka, Y.; Mori, A.;
Hiyama, T. Bull. Chem. Soc. Jpn. 1997, 70, 1943.
(14) Suzuki, M.; Miyaura, N.; Itoh, M.; Brown, H. C.; Holland, G. W.;
Negishi, E. J. Am. Chem. Soc. 1971, 93, 2792.
(15) Miyaura, N.; Tanabe, Y.; Suginome, M.; Suzuki, A. J. Organomet.
Chem. 1982, 233, C13.
(20) Compound 3b was synthesized by epoxidation of 5,5-dimethyl-1,3-
cyclopentadiene. (a) Crandall, J. K.; Banks, D. B.; Colyer, R. A. J. Org.
Chem. 1968, 33, 423. (b) Smith, W. T.; McLeod, G. L. Organic Syntheses;
Schreiber, R. S., Ed.; J. Wiley: New York, 1951; Vol. 31, p 40. (c) Holder,
R. W.; Daub, J. P.; Baker, W. E.; Gilbert, R. H., III; Graf, N. A. J. Org.
Chem. 1982, 47, 1445.
(16) Mikhailov, B. M.; Bubnov, Y. N.; Tsyban, A. V. J. Organomet.
Chem. 1978, 154, 113.
(21) Ross, A. M.; Pohl, T. M.; Piazza, K.; Thomas, M.; Fox, B.; Whalen,
D. L. J. Am. Chem. Soc. 1982, 104, 1658.
3898
Org. Lett., Vol. 2, No. 24, 2000

approach to cis-9a by allylboration of 1,3-cyclohexadiene
with allyldibromoborane was reported.22
Allylboration of epoxides 12a and 12b derived from
acyclic 1,3-dienes was slower compared tothat of 8a and 8b
(Table 4). The reaction required several days when carried
Table 2. Allylboration of 8a-c with 1
Table 4. Allylboration of 12a and 12b with 1 and 2
product
compositiona (%)
9 (c/t)c 10 (c/t)c 11
temp time
yieldb
(%)
epoxide solvent (°C)
(h)
8a
8a
8b
8b
8c
Et2O
THF
Et2O
THF
neat
20
20
20
65
120
5
81(72/28) 19(63/37)
82
69
78
68
65
24 82(63/37) 16(56/44)
24 68(62/38) 32(41/59)
12 59(60/40) 39(43/57)
14 52(62/38) 48(52/48)
2
2
a Determined by GC analysis. b Isolated yields. c The cis/trans ratio was
established by hydrogenation to cis/trans 2- and 4-propyl-cyclohexanols
and comparison with authentic samples by GC.
temp time
epoxide reagent (°C) (h)
product compositiona (E/Z)
yieldb
(%)
(%)
12a
12a
12b
12a
12b
1
1
1
2
2
20
60
60
60
80
168 13a 34 14a 66(88/12)
24 13a 46 14a 52(80/20) 15a 2
24 13b 30 14b 66(84/16) 15b 4
48 16a 46 17a 54(78/22)
62
69
65
58
65
room temperature, whereas 3,4-epoxycyclooctene required
prolonged heating under neat conditions.
The 1,2-addition of 1 to these epoxides is favored over
1,4-addition, and essentially no rearrangement of the ep-
oxides to the corresponding ketones is observed under the
reaction conditions used (Table 2). Noteworthy is the
preferential formation of cis-2-allyl-3-cycloalken-1-ols.
The cis-1,2-addition may be rationalized assuming coor-
dination of boron to oxygen of the vinylic epoxide and
intramolecular transfer of allyl group via a six-membered
transition state. In contrast, other allylmetal reagents, e.g.,
derivatives of magnesium, tin, and copper, react with 8a
producing trans-2-allyl-3-cyclohexen-1-ol or trans-4-allyl-
2-cyclohexen-1-ol (Table 3). Recently, a carbometalation
72 16b 35 17b 65(77/23)
a Determined by GC analysis. Products identified by H and 13C NMR
analysis and by comparison (GC, 1H and 13C NMR) with authentic samples.
b Isolated yields.
1
at room temperature. However, at 60 °C under neat condi-
tions 1 reacted with 12a in 24 h, and 2 required 48 h.
Despite the prolonged reaction time rearrangement of the
epoxides is not a competing reaction since only very small
amounts of rearranged products 15a and 15b were obtained
(Table 4). 1,4-Addition predominates and the ratio of E/Z
isomers is in the range of 80/20.
In conclusion, the allylboration of 3,4-epoxycyclopentene
and its alkyl-substituted derivatives provides a convenient
access to the corresponding acyclic (Z)-trienols in high
stereoselectivity and good yields. The preferential cis-1,2-
addition of 1 to 3,4-epoxycycloalkenes provides cis-2-allyl-
3-cycloalken-1-ols. The stereochemistry of the addition is
opposite to other allylmetal reagents.
Table 3. Reaction of Allylmetal Reagents with 8a
Acknowledgment. Financial support from the State
Committee for Scientific Research, Warsaw, grant TO9A
13809, is acknowledged.
temp
(°C)
time
product
yielda
allyl-M
solvent
(h) composition (%) (%)
Supporting Information Available: Spectroscopic data
for all new products. This material is available free of charge
via the Internet at http://pubs.acs.org.
allylMgBr
allylMgBr
Et2O
Et2O
20
0
4
2
trans-9a
trans-9a (77)
11a (23)
trans-9a
trans-10a
40b
55
allylSnMe3
allylCu(CN)Li THF
CH2Cl2 -78
-40 f rt
0.5
d
40c
66e
OL006641G
a Isolated yields. b Reference 5c. c Reference 6. d Not reported. e Refer-
ence 8c.
(22) (a) Singleton, D. A.; Waller, S. C.; Zhang, Z.; Frantz, D. E.; Leung,
S.-W. J. Am. Chem. Soc. 1996, 118, 9986. (b) Frantz, D. E.; Singleton, D.
A. Org. Lett. 1999, 1, 485.
Org. Lett., Vol. 2, No. 24, 2000
3899