Stereoselective Synthesis of Highly Functionalized Trisubstituted Olefins via the Aldol Reaction of Allenoxyborinates with Carbonyl Compounds

Article abstract of DOI:10.1021/jo990080t

Allenoxyborinates, generated via the reaction of dicyclohexylborane with α,β-acetylenic ketones, react in situ with excess starting ketone to afford stereodefined, functionalized, trisubstituted olefins in good yields. The allenoxyborinates, (RCH=C=C(R′)OB(c-C₆H₁₁)₂, can also be trapped by aldehydes and ketones when R′ is a tert-butyl group.

Full text of DOI:10.1021/jo990080t

5822
J . Org. Chem. 1999, 64, 5822-5825
Ster eoselective Syn th esis of High ly F u n ction a lized Tr isu bstitu ted
Olefin s via th e Ald ol Rea ction of Allen oxybor in a tes w ith Ca r bon yl
Com p ou n d s
Su Yu, Nan-Sheng Li, and George W. Kabalka*
Departments of Chemistry and Radiology, The University of Tennessee, Knoxville, Tennessee 37996-1600
Received J anuary 15, 1999
Allenoxyborinates, generated via the reaction of dicyclohexylborane with R,â-acetylenic ketones,
react in situ with excess starting ketone to afford stereodefined, functionalized, trisubstituted olefins
in good yields. The allenoxyborinates, (RCHdCdC(R′)OB(c-C6H11)2, can also be trapped by aldehydes
and ketones when R′ is a tert-butyl group.
In tr od u ction
in a number of transformations leading to natural
products10 and have remained an active area of research
for organic chemists.11 We now wish to report the details
of this novel one-pot synthesis of stereodefined, highly
functionalized, trisubstituted olefins via the reaction of
R,â-acetylenic ketones with dicyclohexylborane.
Hydroboration plays an important role in organic
synthesis.1 Recently we reported that the carbon-carbon
double bonds and triple bonds of nonconjugated unsatu-
rated ketones and aldehydes can be selectively hydro-
borated by dicyclohexylborane.2 However, the reactions
of R,â-unsaturated ketones and aldehydes with borane
reagents proceed differently. For example, conjugated
olefinic ketones react stereoselectively with dicyclohexyl-
borane or (-)-diisopinocampheylborane to form boron
enolates,3 whereas the carbonyl group in R,â-unsaturated
ketones is simply reduced by 9-BBN.4 Enantioenriched
propargylic alcohols are obtained by reduction of R,â-
acetylenic ketones using chiral boron reagents such as
â-isopinocampheyl-9-BBN,5 B-chlorodiisopinocampheyl-
borane6 and BMS in the presence of chiral B-methyl-
4,5,5-triphenyl-1,3,2-oxazaborolidine.7
Resu lts a n d Discu ssion s
We found that the reaction of a molar equivalent of
3-heptyn-2-one with dicyclohexylborane yields a complex
mixture of products. On the other hand, when 2 molar
equiv of 3-heptyn-2-one are added to 1 molar equiv of
dicyclohexylborane in THF at 0 °C, (Z)-3-butylene-4-
hydroxy-4-methylnon-5-yn-2-one (2a ) is isolated in good
yield, as shown in Scheme 1. In an effort to optimize the
reaction conditions, the effects of reaction temperature,
solvent, and stoichiometry were studied. The reaction
produced 2a in 45% yield after 1 h at room temperature
but required 2 h at 0 °C. No reaction occurred overnight
at -78 °C. Thus, room temperature was chosen for
We recently reported that dicyclohexylborane reacts
with R,â-acetylenic ketones to form trisubstituted alkenes
stereoseletively.8 Trisubstituted olefins are present in
many naturally occurring biologically active compounds
such as terpenoids, pheromones, macrolide antibiotics,
marine products, etc.9 They are also key intermediates
(9) (a) Marfat, A.; McGuirk, P. R.; Helquist, P. J . Org. Chem. 1979,
44, 3888. (b) Fenical, W. Chem. Rev. 1993, 93, 1673. (c) Garson, M. J .
Chem. Rev. 1993, 93, 1699. (d) D’Auria, M. V.; Minale, L.; Riccio, R.
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Palmer, T.; Kishi, Y. J . Am. Chem. Soc. 1978, 100, 2933. (b) Corey, E.
J .; Katazenellenbogen, J . A.; Gilman, N. W.; Roman, S. A.; Erickson,
B. W. J . Am. Chem. Soc. 1968, 90, 5618. (c) Bauchat, P.; Le Rouille,
E.; Foucaud, A. Bull. Chim. Soc. Fr. 1991, 267. (d) Buchholz, R.;
Hoffman, H. M. R. Helv. Chim. Acta 1991, 74, 1213. (e) Charette, A.
B.; Cote, B. Tetrahedron Lett. 1993, 34, 6833. (f) Roush, W. R.; Brown,
B. B. J . Org. Chem. 1993, 58, 2151. (g) Perlmutter, P.; Tabone, M. J .
Org. Chem. 1995, 60, 6515. (h) Marson, C. M.; Harper, S.; Oare, C. A.;
Walsgrove, T. J . Org. Chem. 1998, 63, 3798.
(1) (a) Gragg, G. M. L. Organoboranes in Organic Synthesis; Marcel
Dekker: New York, 1973; pp 137-197. (b) Pelter, A.; Smith K.; Brown,
H. C. Borane Reagents; Academic Press: London, 1988; pp 165-205.
(c) Evans, D. A.; Fu, G. C. J . Am. Chem. Soc. 1992, 114, 6671. (d)
Evans, D. A.; Fu, G. C.; Hoveyda, A. H. J . Am. Chem. Soc. 1992, 114,
6671. (e) Fisher, G. B.; Goralski, C. T.; Nicholson, L. W.; Hasha, D. L.;
Zakett, D.; Singaram, B. J . Org. Chem. 1995, 60, 2026. (f) Fugami, K.;
Hagiware, N.; Okeda, T.; Kosugi, M. Chem. Lett. 1998, 81. (g)
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(2) (a) Kabalka, G. W.; Yu, S.; Li, N.-S. Tetrahedron Lett. 1997, 38,
5455. (b) Kabalka, G. W.; Yu, S.; Li, N.-S. Tetrahedron Lett. 1997, 38,
7681. (c) Kabalka, G. W.; Yu, S.; Li, N.-S. Can. J . Chem. 1998, 76,
800.
(3) (a) Boldrini, G. P.; Marcini, F.; Tagliavini, E.; Trombini, C.;
Umani-Ronchi, A. J . Chem. Soc., Chem. Commun. 1990, 1680. (b)
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Ronchi, A. Tetrahedron Lett. 1991, 32, 1229.
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J . I.; Gabriel, J . J . Org. Chem. 1989, 54, 159.
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(11) (a) For a review, see: Faulkner, D. J . Synthesis 1971, 175. For
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Urabe, H.; Sato, F. J . Org. Chem. 1995, 60, 290. (f) Deloux, L.; Srebnik,
M.; Sabat, M. J . Org. Chem. 1995, 60, 3276. (g) Zhang, Q.; Yang, Y.;
Martin, A. R. Tetrahedron Lett. 1993, 34, 2235. (h) Yang, G.; Myles,
D. C. Tetrahedron Lett. 1994, 35, 2503. (i) Evans, D. A.; Carreira, E.
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1995, 60, 4635. (k) Deng, M.; Tang, Y.; Xu, W. Tetrahedron Lett. 1984,
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10.1021/jo990080t CCC: $18.00 © 1999 American Chemical Society
Published on Web 07/14/1999

Synthesis of Trisubstituted Olefins
J . Org. Chem., Vol. 64, No. 16, 1999 5823
Sch em e 1
Sch em e 2
Ta ble 1. Rea ction of r,â-Acetylen ic Keton es w ith
Dicycloh exylbor a n e
yields except in the case of 2,2-dimethylnon-4-yn-3-one
(Table 1, entry 8).
In the reaction of 4,11-pentadecadiyn-6,10-dione with
dicyclohexylborane (Table 1, entry 7), an intermolecular
reaction competed with the desired intramolecular reac-
tion. The reaction was then carried out at various
concentrations of 4,11-pentadecadiyn-6,10-dione. As an-
ticipated, diluting the reactants increased the yield of
desired intramolecular product.
Interestingly, the 1H and 13C NMR spectra revealed
that only one product formed in each of the reactions.
The stereochemistry of the alkene products was deter-
mined to be Z using NOESY NMR. The mechanism of
the reaction is presumed to involve the hydroboration of
the triple bond followed by enolization of the intermediate
vinylborane 3 to produce allenoxyborinate 4, Scheme 2.
The allenoxyborinate then undergoes an aldol reaction
with excess R,â-acetylenic ketone to give the (Z)-olefin.
Reactions of allenoxyborinates with other electrophiles,
namely, aldehydes, ketones, and acid halides, were also
investigated. When aldehydes were used as electrophiles,
mixtures were produced containing products generated
by reaction of the allenoxyborinates with the added
aldehyde as well as aldehyde reduction products. How-
ever when alkyl ketones or acid chlorides were used, only
the aldol product generated by reaction of the allenoxy-
borinate with excess R,â-acetylenic ketone was formed.
These results suggest that the R,â-acetylenic ketones are
less reactive toward allenoxyborinates than aldehydes
but are more reactive than alkyl ketones and acid
chlorides.
As noted in Table 1 (entry 8), the reaction of 2,2-
dimethylnon-4-yn-3-one with dicyclohexylborane did not
form the self-condensation product. To demonstrate that
the expected allenoxyborinate did indeed form, 1 molar
equiv of 2,2-dimethylnon-4-yn-3-one was allowed to react
with 1.25 molar equiv of dicyclohexylborane in THF at
room temperature for 1 h; the reaction mixture was then
oxidized using sodium perborate. Both (E)- and (Z)-2,2-
dimethylnon-4-en-3-one were obtained in an overall 60%
yield. This result suggests that the allenoxyborinate
intermediate formed but did not undergo aldol condensa-
tion with excess ketone. Interestingly, 5-cyclohexyl-5-
hydroxy-2,2-dimethyl-3-nonanone (∼30%) was also ob-
tained. Presumably, it formed via the rearrangement of
the isomeric vinylborane intermediate generated during
hydroboration of carbon-carbon triple bond.
a
Reactions were run using 2 mmol R,â-acetylenic ketones and
b
1.25 mmol dicyclohexylborane in THF. All new compounds were
characterized by spectral and elemental analysis. c Isolated yield
d
based on ketone. None of the desired product was obtained.
Since the allenoxyborinate generated by reaction of
dicyclohexylborane to 2,2-dimethylnon-4-yn-3-one was
stable at room temperature, we felt it might be possible
to trap it using added electrophiles. The reaction of 2,2-
dimethylnon-4-yn-3-one with dicyclohexyborane in THF,
followed by the addition of benzaldehyde, gave the mixed
aldol product. The reaction of 1 molar equiv of 2,2-
dimethylnon-4-yn-3-one with dicyclohexylborane, fol-
lowed by reaction with benzaldehyde, gave the expected
aldol product in 50% yield. Using 2 molar equiv of 2,2-
further studies. The studies revealed that solvents (THF,
CH2Cl2, and pentane) had little effect on the reaction of
R,â-acetylenic ketones with dicyclohexylborane, and op-
timum yields were obtained when a slight excess of
dicyclohexylborane was utilized.
A variety of R,â-acetylenic ketones was then allowed
to react with dicyclohexyl-borane in THF at room tem-
perature. The results are presented in the Table 1. As
shown, the expected products were obtained in good

5824 J . Org. Chem., Vol. 64, No. 16, 1999
Yu et al.
was distilled over P2O5. 3-Heptyn-2-one,12 4,4-dimethyl-1-
phenylpent-2-yn-1-one14 and 1-phenylhex-2-yn-1-one13 were
prepared via the reaction of alkynyllithium reagents with N,N-
dialkylcarboxamides.14 2,2-Dimethylnon-4-yn-3-one, 4-methyl-
1-phenylpent-1-yn-3-one,15 1-cyclopropylhex-2-yn-1-one, 4,11-
pentadecadiyn-6,10-dione were prepared via the reaction of
alkynylzinc reagents with acid chlorides.16 Borane reagents,
n-butyllithium, acid chloride, and anhydrous zinc chloride were
used as received (Aldrich Chemical Co.). Alkynes, N,N-
dimethylacetamide, N,N-dimethylbenzamide, 4-phenyl-3-bu-
tyn-2-one, and cyclohexene were purified by distillation prior
to use. Reactions were monitored by TLC. Products were
purified by flash chromatography. 1H NMR and 13C NMR
spectra were recorded at 250 and 62.5 MHz, respectively.
NOESY spectra were recorded in CDCl3 using TMS as the
internal standard at 400 MHz (D1 ) 3.0 s, P1 ) 8.4 s).
Elemental analyses were performed by Atlantic Microlab Inc.,
Norcross, Georgia.
Ta ble 2. Syn th esis of
2,2-Dim eth yl-4-(1-h yd r oxya lk yl)-4-n on en -3-on ea
Gen er a l P r oced u r e for th e Rea ction of r,â-Acetylen ic
Keton es w ith Dicycloh exylbor a n e. Th e Syn th esis of (Z)-
3-Bu tylen e-4-h ydr oxy-4-m eth yln on -5-yn -2-on e (2a) Is Rep-
r esen ta tive. Borane (1.25 mmol, 1.25 mL of a 1.00 M solution
in THF) was placed in a dry, argon-flushed, round-bottomed
flask which was immersed in an ice-water bath. Cyclohexene
(2.5 mmol, 0.21 g, 0.25 mL) was added dropwise and the
mixture stirred at 0 °C for 1 h. 3-Heptyn-2-one (2.0 mmol, 0.22
g) was then added to the slurry of dicyclohexylborane in THF.
The cooling bath was removed and the mixture stirred for 1 h
at room temperature. Methanol (2.0 mL) was added to quench
the reaction, the organic solvents were removed under reduced
pressure, and 3-butylene-4-hydroxy-4-methylnon-5-yn-2-one
(0.14 g, 62% yield) was obtained by flash chromatography. 1H
NMR δ 0.93 (t, J ) 7.3 Hz, 3H), 1.50 (m, 4H), 1.63 (s, 3H),
2.09 (q, J ) 7.4 Hz, 2H), 2.20 (t, J ) 7.3 Hz, 2H), 2.42 (s, 3H),
3.35 (s, 1H), 6.04 (t, J ) 7.7, 1H); 13C NMR δ 13.4, 13.6, 20.5,
21.9, 22.4, 29.8, 31.1, 32.9, 68.8, 82.6, 85.6, 130.5, 145.4, 207.2.
Anal. Calcd for C14H22O2: C, 75.63; H, 9.97. Found: C, 75.83;
H, 10.03.
(Z)-3-Ben zylid en -4-h yd r oxy-4-m et h yl-6-p h en ylh ex-5-
yn -2-on e (2b). 2b was prepared via the reaction of 4-phenyl-
but-3-yn-2-one (2.0 mmol, 0.29 g, 0.29 mL) with dicyclohexy-
borane (1.25 mmol) in 72% yield using the general procedure
outlined for 2a . 1H NMR δ 1.88 (s, 3H) 2.13 (s, 3H), 3.95 (s,
1H), 7.23-7.35 (m, 9H), 7.41-7.45 (m, 2H); 13C NMR δ 29.0,
32.3, 69.6, 85.1, 90.6, 122.1, 128.2, 128.6, 128.7, 129.3, 131.6,
135.1, 144.9, 208.8. Anal. Calcd for C20H18O2: C, 82.73; H, 6.25.
Found: C, 82.54; H, 6.33.
a
Reactions were carried out using 2.5 mmol dicyclohexylborane,
2.0 mmol 2,2-dimethylnon-4-yn-3-one and 1.0 mmol of electro-
b
philes. All new compounds were characterized by spectral and
elemental analysis. c Isolated yields based on electrophiles.
dimethylnon-4-yn-3-one and dicyclohexylborane and then
adding 1 equiv of benzaldehyde resulted in a quantitative
formation of the aldol product, based on benzaldehyde.
A variety of ketones and aldehydes was allowed to
react with the allenoxyborinate generated by the reaction
of 2,2-dimethylnon-4-yn-3-one with dicyclohexylborane
(Table 2). As can be seen, the reaction of the allenoxy-
borinate with an aldehyde or ketone forms the expected
aldol product in good yields. However, this allenoxybori-
nate does not react with acid chlorides.
(Z)-2-Bu t ylen e-3-h yd r oxy-1,3-d ip h en yloct -4-yn -1-on e
(2c). 2c was prepared via the reaction of 1-phenylhex-2-yn-
1-one (2.0 mmol, 0.34 g) with dicyclohexylborane (1.25 mmol)
1
in 78% yield using the general procedure outlined for 2a . H
NMR δ 0.71 (t, J ) 7.3 Hz, 3H), 0.86 (t, J ) 7.3 Hz, 3H), 1.27
(m, 2H), 1.40 (m, 2H), 1.73 (q, J ) 7.4 Hz, 2H), 2.13 (t, J ) 7.0
Hz, 2H), 4.49 (s, 1H), 6.00 (t, J ) 7.8 Hz, 1H), 7.23-7.42 (m,
5H), 7.50-7.53 (m, 1H), 7.63-7.67 (m, 2H), 7.80-7.84 (m, 2H);
13C NMR 13.4, 20.6, 21.7, 22.0, 31.6, 74.6, 81.8, 88.4, 126.4,
127.5, 127.8, 128.3, 129.5, 133.4, 134.0, 137.7, 141.8, 142.4,
200.5. Anal. Calcd for C24H26O2: C, 83.20; H, 7.56; Found: C,
83.14; H, 7.55.
Con clu sion
A stereoselective synthesis of highly functionalized
trisubstituted olefins has been developed. Dicyclohexyl-
borane adds to R,â-acetylenic ketone to generate allen-
oxyborinates which then react with excess R,â-acetylenic
ketone. Stereodefined, functionalized trisubstituted ole-
fins having the Z configuration are obtained in good
yields. The sterically hindered allenoxyborinate which is
generated from the reaction of 2,2-dimethylnon-4-yn-3-
one with dicyclohexylborane can also be trapped by
aldehydes and ketones to form (Z)-trisubstituted olefins.
(Z)-4-Ben zylid en e-5-h yd r oxy-5-isop r op yl-2-m et h yl-7-
p h en ylh ep t-6-yn -3-on e (2d ). 2d was prepared via the reac-
tion of 2-methyl-5-phenylpent-4-yn-3-one (2.0 mmol, 0.34 g)
with dicyclohexylborane (1.25 mmol) in 72% yield using the
1
general procedure outlined for 2a . H NMR δ 0.94 (d, J ) 6.8
Hz, 3H), 0.99 (d, J ) 6.8 Hz, 3H), 1.12 (d, J ) 6.8 Hz, 3H),
1.19 (d, J ) 6.6 Hz, 3H), 2.48 (m, 2H), 3.40 (s, 1H), 7.21-7.36
(m, 8H), 7.39 (s, 1H), 7.47-7.51 (m, 2H); 13C NMR δ 17.0, 18.3,
18.7, 37.0, 41.6, 78.5, 87.6, 88.4, 122.3, 128.2, 128.4, 128.5,
Exp er im en ta l Section
(12) House, H. O. J . Am. Chem. Soc. 1972, 94, 8471.
(13) Ma, D. W.; Yu, Y.; Lu, X. J . Org. Chem. 1989, 54, 1105.
(14) Guerin, B.; J ohnston, L. J . J . Org. Chem. 1989, 54, 3176.
(15) Verkruijsse, H. D.; Heus-Kloos, Y. A.; Brandsma, L. J . Organo-
metallic Chem. 1988, 338, 289
All reagents and solvents were transferred using techniques
designed to eliminate contact with air. All glassware, syringes,
and needles were oven-dried at 250 °C for at least 12 h prior
to use. THF was distilled over sodium benzophenone ketyl.
Pentane was dried and distilled over calcium hydride. CH2Cl2
(16) Barbee, T. R.; Albizati, K. F. J . Org. Chem. 1991, 56, 6764.

Synthesis of Trisubstituted Olefins
J . Org. Chem., Vol. 64, No. 16, 1999 5825
128.7, 131.6, 132.8, 135.7, 143.7, 213.6. Anal. Calcd for
(Z)-4-(1-Hyd r oxyp h en ylm eth yl)-2,2-d im eth yln on -4-en -
3-on e (5b). 5b was prepared via the reaction of benzaldehyde
(1.0 mmol, 0.11 g, 0.10 mL) with the allenoxyborinate, which
was generated using the general procedure. The product was
obtained in 100% yield. 1H NMR δ 0.84 (t, J ) 7.0 Hz, 3H),
1.11 (s, 9H), 1.20-133 (m, 4H) 1.89 (q, J ) 7.2 Hz, 2H), 2.91
(d, J ) 5.1 Hz, 1H), 5.28 (dt, J ) 7.6 Hz, 1.2 Hz, 1H), 5.36 (d,
J ) 5.1 Hz, 1H), 7.26-7.33 (m, 5H); 13C NMR δ 13.7, 22.2,
27.1, 27.2, 29.8, 31.2, 43.8, 75.3, 126.9, 127.7, 128.2, 130.1,
141.4, 144.5, 217.2. Anal. Calcd for C18H26O2: C, 78.79; H, 9.55.
Found: C, 78.69; H, 9.65.
C
24H26O2: C, 83.20; H, 7.56. Found: C, 82.92; H, 7.70.
(Z)-2-(2,2-Dim eth ylp r opyliden e)-3-h ydr oxy-6,6-dim eth -
yl-1,3-d ip h en ylh ep t-4-yn -1-on e (2e). 2e was prepared via
the reaction of 4,4-dimethyl-1-phenylpent-2-yn-1-one (2.0 mmol,
0.37 g) with dicyclohexylborane (1.25 mmol) in 78% yield using
the general procedure outlined for 2a . 1H NMR δ 0.88 (s, 9H),
1.01 (s, 9H), 3.57 (s, 1H), 5.85 (s, 1H) 7.20-741 (m, 5H), 7.47-
7.53 (m, 1H), 7.60-7.63 (m, 2H), 7.90-7.93 (m, 2H); 13C NMR
δ 27.2, 29.8, 30.3, 30.3, 33.5, 74.3, 80.7, 96.8, 126.5, 127.6,
127.7, 128.0, 129.9, 133.1, 138.7, 141.1, 142.8. Anal. Calcd for
C
26H30O2: C, 83.38; H, 8.07. Found: C, 83.15; H, 8.01.
(Z)-(1-Hyd r oxy-1-m eth ylp en tyl)-2,2-d im eth yln on -4-en -
3-on e (5c). 5c was prepared via the reaction of 2-hexanone
(1.0 mmol, 0.10 g, 0.12 mL) with the allenoxyborinate, which
was generated using the general procedure. The product was
obtained in 100% yield. 1H NMR δ 0.85-0.93 (m, 6H), 1.20 (s,
9H), 1.30-1.33 (m, 8H), 1.38 (s, 3H) 1.61-1.62 (m, 2H), 1.78
(br s, 1H), 1.90 (q, J ) 7.2 Hz, 2H), 5.25 (t, J ) 7.5 Hz, 1H);
13C NMR δ 13.8, 14.0, 22.2, 22.9, 25.9, 27.5, 27.6, 28.6, 29.9,
31.5, 43.1, 43.8, 74.6, 124.9, 148.5, 219.0. Anal. Calcd for
(Z)-2-Bu tylen e-1,3-d icyclop r op yl-3-h yd r oxyoct-4-yn -1-
on e (2f). 2f was prepared via the reaction of 1-cyclopropylhex-
2-yn-1-one (2.0 mmol, 0.27 g) with dicyclohexylborane (1.25
mmol) in 66% yield via the general procedure outlined for 2a .
1H NMR δ 0.48-0.52 (m, 3H), 0.72 (m, 1H), 0.92-1.05 (m, 8H),
1.20-1.28 (m, 4H), 1.45-1.57 (m, 4H), 2.16-2.29 (m, 4H), 3.89
(s, 1H), 8.26 (t, J ) 7.8 Hz, 1H); 13C NMR δ 2.2, 2.4, 12.9,
13.3, 13.6, 19.7, 20.5, 21.9, 22.4, 23.5, 31.0, 73.8, 78.7, 86.6,
131.7, 144.8, 210.0. Anal. Calcd for C18H26O2: C, 78.79; H, 9.55.
Found: C, 78.84; H, 9.59.
C
17H32O2: C, 76.07; H, 12.01. Found: C, 76.22; H, 11.89.
(Z)-2-B u t y le n e -3-h y d r o x y -3-p e n t -1-y n y lc y c lo h e x -
a n on e (2g). 2g was prepared via the reaction of 4,11-
pentadecadiyn-6,10-dione (1.0 mmol, 0.23 g) with dicyclohexyl-
borane in THF (10 mL) using the general procedure outlined
for 2a . The product was obtained in 55% yield. 1H NMR δ 0.91
(t, J ) 7.3 Hz, 3H), 0.99 (t, J ) 7.3 Hz, 3H), 1.26 (m, 1H),
1.40-1.59 (m, 4H), 1.92-2.56 (m, 10H), 6.33 (t, J ) 7.4 Hz,
1H); 13C NMR δ 13.3, 13.7, 19.5, 20.6, 21.9, 22.5, 30.5, 39.5,
42.2, 72.5, 81.3, 87.7, 136.8, 141.3, 202.9. Anal. Calcd for
(Z)-4-(1-H yd r oxycycloh exyl)-2,2-d im et h yln on -4-en -3-
on e (5d ). 5d was prepared via the reaction of cyclohexanone
(1.0 mmol, 0.10 g, 0.10 mL) with the allenoxyborinate, which
was generated using the general procedure. The product was
obtained in 100% yield. 1H NMR δ 0.88 (t, J ) 7.0 Hz, 3H),
1.08-1.14 (m, 2H), 1.20 (s, 9H), 1.27-1.37 (m, 4H), 1.52-1.58
(m, 6H), 1.81-1.94 (m, 5H), 5.36 (t, J ) 7.5 Hz, 1H); 13C NMR
δ 13.8, 21.7, 22.2, 25.3, 27.6, 29.9, 31.5, 38.3, 43.7, 73.1, 124.6,
150.4, 219.3. Anal. Calcd for C17H30O2: C, 76.64; H, 11.35.
Found: C, 76.44; H, 11.21.
C
15H22O2: C, 76.88; H, 9.46. Found: C, 76.79; H, 9.43.
Gen er a l P r oced u r e for th e Rea ction of 2,2-Dim eth yl-
(Z)-4-(1-Hyd r oxy-1-p h en yleth yl)-2,2-d im eth yln on -4-en -
3-on e (5e). 5e was prepared via the reaction of acetophenone
(1.0 mmol, 0.12 g, 0.12 mL) with the allenoxyborinate, which
was generated using the general procedure. The product was
obtained in 100% yield. 1H NMR δ 0.86 (t, J ) 7.0 Hz, 3H),
1.01 (s, 9H), 1.21-1.35 (m, 4H), 1.70 (s, 3H), 1.86-1.96 (m,
2H), 3.22 (s, 1H), 5.40 (t, J ) 7.6 Hz, 1H), 7.19-7.34 (m, 3H),
7.45-7.49 (m, 2H); 13C NMR δ 13.7, 22.1, 27.2, 30.2, 30.4, 31.2,
43.9, 76.0, 125.8, 126.9, 127.8, 127.9, 146.2, 147.3, 219.6. Anal.
Calcd for C19H28O2: C, 79.13; H, 9.78; Found: C, 79.13; H,
9.92.
n on -4-yn -3-on e w ith Dicycloh exylbor a n e, F ollow ed by
Tr a p p in g th e Allen oxybor in a te w ith Ca r bon yl Com -
p ou n d s. Th e Syn th esis of (Z)-4-(1-Hyd r oxyp r op yl)-2,2-
d im eth yln on -4-en -3-on e (5a ) Is Rep r esen ta tive. Borane
(2.5 mmol, 2.5 mL of a 1.0 M solution in THF) was placed in
a dry, argon-flushed, round-bottomed flask which was then
immersed in an ice-water bath. Cyclohexene (5.0 mmol, 0.41
g, 0.51 mL) was added dropwise, and the mixture was stirred
at 0 °C for 1 h to generate dicyclohexylborane. 2,2-Dimethyl-
non-4-yn-3-one (2.0 mmol, 0.33 g) was then added to the slurry
of dicyclohexylborane in THF. The cooling bath was removed,
and the mixture was stirred at room temperature. After the
white precipitate disappeared, propanal (1.0 mmol, 0.06 g, 0.07
mL) was added. The mixture was stirred at room temperature
for an additional hour. Then methanol (2.0 mL) was added to
quench the reaction. The organic solvent was removed under
reduced pressure and 2,2-dimethyl-4-(1-hydroxypropyl)non-4-
en-3-one (0.22 g, 100% yield) was obtained by flash chroma-
Ack n ow led gm en t. We wish to thank the Depart-
ment of Energy and the Robert H. Cole Foundation for
their support of this research. We also want to thank
Dr. Hong J un Pan for carrying out the NMR NOESY
experiments.
1
tography. H NMR δ 0.88 (t, J ) 6.8 Hz, 3H), 0.96 (t, J ) 7.3
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra of 2a -g, 5a -e, and COSY and NOESY spectra of 2a
and 5a . This material is available free of charge via the
Internet at http://pubs.acs.org.
Hz, 3H), 1.20 (s, 9H), 1.23-1.39 (m, 4H), 1.51 (m, J ) 1H),
1.64 (m, 1H). 1.91 (q, J ) 7.0 Hz, 2H), 2.21 (br s, 1H), 4.16 (m,
1H), 5.52 (t, J ) 7.5 Hz, 1H); 13C NMR δ 9.8, 13.8, 22.2, 27.1,
27.2, 29.2, 29.7, 31.5, 43.9, 73.9, 127.5, 144.9, 217.1. Anal.
Calcd for C14H26O2: C, 74.28; H, 11.58. Found: C, 74.11; H,
11.43.
J O990080T