Asymmetric reduction. A convenient method for the reduction of alkynyl ketones

Full text of DOI:10.1021/jo951712o

3214
J . Org. Chem. 1996, 61, 3214-3217
Sch em e 1
Asym m etr ic Red u ction . A Con ven ien t
Meth od for th e Red u ction of Alk yn yl
Keton es
Kathlyn A. Parker* and Mark W. Ledeboer†
Department of Chemistry, Brown University, Providence,
Rhode Island 02912
Received September 19, 1995 (Revised Manuscript Received
February 22, 1996)
In order to prepare a cyclic enediynediol for attachment
to biopolymers, we required a method for the asymmetric
reduction of alkyl alkynyl ketones. In the system of
interest, both Alpineborane1 and Binal-H2 gave unsatis-
factory results. We postulated that the long reaction
times required for reduction by these reagents allowed
for the competitive degradation of our substrate. We
therefore sought an alternative reagent which would
effect the desired chiral reduction rapidly at low tem-
perature.3
Sch em e 2
Since the initial reports by Itsuno4 on the chiral
reduction of ketones by borane in the presence of an
amino acid, numerous papers have described similar
reductions by borane in the presence of chiral oxazaboro-
lidine catalysts.5 Although these reagents have been
applied to produce a wide variety of chiral alcohol
structures, to date this methodology has not been applied
to the reduction of alkynyl ketones.
Sch em e 3
We have found that the reduction of conjugated alkynyl
ketones 1 with borane methyl sulfide complex (BMS) in
the presence of chiral oxazaborolidine 2 (derived from
R,R-diphenyl-L-prolinol) affords propargyl alcohols 3 in
a reaction which is both enantioselective and relatively
fast at low temperature (Scheme 1). We have now
assigned the configuration of these alcohols (see below)
as S.
Of the ketones chosen for study only 5-phenyl-4-butyn-
3-one (1a ) was commercially available.7 Phenyl alkynyl
ketones 1b-e were conveniently obtained by the two-
step sequence shown in Scheme 2. Thus, addition of an
aldehyde to lithiated phenylacetylene yielded the racemic
propargyl alcohol. Subsequent oxidation of the crude
material with manganese dioxide generated the desired
ketones in moderate-to-good yields.
Model systems for the study of the reduction of
terminal alkynyl ketones were obtained most efficiently
according to literature procedures (Scheme 3).8 Thus,
ynones 1f and 1g were prepared by treating the com-
mercially available acid chlorides with bis(trimethylsilyl)-
acetylene (BTMSA) in the presence of aluminum chloride
followed by desilylation of the Friedel-Craft product.
Asym m etr ic Red u ction Stu d ies. Reactions were
performed on approximately 50 mg of ketone in THF. The
mole equivalents of oxazaborolidine 2 and BMS and the
temperature were varied. The asymmetric reductions of
phenyl alkynyl ketones 1a -e were complete in less than
1 h at -30 °C.
P r ep a r a tion of Su bstr a tes a n d Rea gen ts. The
oxazaborolidine 2 could be prepared just prior to reaction
and used without purification. Alternatively, if a larger
quantity of reagent was desired for use at a later date,
the reagent could be purified by vacuum distillation and
stored according to the procedure described by Mathre,
J ones, Blacklock, et al.6
† Government Assistance in Areas of National Need Fellow, 1993-
95; Corinna Borden Keen Fellow, 1995-96.
(1) For a review of Alpineborane reductions, see: Midland, M. M.;
Tramontano, A.; Kazubski, A. Graham, R. S.; Tsai, D. J . S.; Cardin,
D. B. Tetrahedron 1984, 40, 1371.
(2) (a) Nishizawa, M.; Yamada, M.; Noyori, R. Tetrahedron Lett.
1981, 22, 247. (b) Noyori, R.; Tomino, I.; Tanimoto, Y.; Nishizawa, M.
J . Am. Chem. Soc. 1984, 106, 6709.
(3) The complementary approach, enantioselective addition of an
acetylide to an aldehyde, was not necessarily compatible with our
overall scheme. For the enantioselective alkynylation of aldehydes,
see: Corey, E. J .; Cimprich, K. A. J . Am. Chem. Soc. 1994, 116, 3151.
(4) (a) Itsuno, S.; Ito, K.; Hirao, A.; Nakahama, S. J . Chem. Soc.,
Chem. Commun. 1983, 469. (b) Itsuno, S.; Ito, K.; Hirao, A.; Nakahama,
S. J . Org. Chem. 1984, 49, 555. (c) Itsuno, S.; Nakano, M.; Miyazaki,
K.; Masuda, H.; Ito, K.; Hirao, A.; Nakahama, S. J . Chem. Soc., Perkin
Trans. 1 1985, 2039.
(5) (a) Corey E. J .; Bakshi, R. K.; Shibata, S. J . Am. Chem. Soc.
1987, 109, 5551. (b) For an extensive review with 74 references see:
Wallbaum, S.; Martens, J . Tetrahedron Asymmetry 1992, 3, 1475. (c)
Corey, E. J .; Azimioara, M.; Sarshar, S. Tetrahedron Lett. 1992, 33,
3429. (d) J ones, D. K.; Liotta, D. C.; Shinkai, I.; Mathre, D. J . J . Org.
Chem. 1993, 58, 799.
The reduction, performed with either stoichiometric or
catalytic amounts of oxazaborolidine 2, provided excellent
yields of the propargyl alcohols. Enantiomeric excesses
were determined by calculation of the integrals of the
(7) Ketone 1a was purchased from the Aldrich Chemical Co. Ketones
1b,d -g and alcohols 3a -d ,f,g are known compounds (see Table 1 for
references).
(6) Mathre, D. J .; J ones, T. K.; Xavier, L. C.; Blacklock, T. J .;
Reamer, R. A.; Mohan, J . J .; Turner J ones, E. T.; Hoogsteen, K.; Baum,
M. W.; Grabowski, E. J . J . J . Org. Chem. 1991, 56, 751.
(8) (a) Schwab, J . M.; Lin, D. C. T. J . Am. Chem. Soc. 1985, 107,
6046. (b) Walton, D. R. M.; Waugh, F. J . Organomet. Chem. 1972, 37,
45.
S0022-3263(95)01712-9 CCC: $12.00 © 1996 American Chemical Society

Notes
J . Org. Chem., Vol. 61, No. 9, 1996 3215
NMR spectra of the corresponding Mosher esters.9 In
all cases, the results (yield and enantiomeric excesses)
obtained with reagent prepared immediately prior to
reduction were comparable to those obtained with re-
agent which had been stored.
The enantiomeric excess of the product alcohol was
significantly larger when an excess of the oxazaborolidine
2 was used. For example, the reduction of ketone 1e at
-30 °C with 5 mol equiv of BMS in the presence of 0.5
mol equiv of oxazaborolidine 2 provided alcohol 3e in 86%
enantiomeric excess (entry 11, Table 1). However, the
same reaction with 2 mol equiv of the reagent, under
otherwise identical conditions, gave a 96% enantiomeric
excess (entry 13, Table 1).
F igu r e 1.
Sch em e 4
Ta ble 1. Red u ction of Alk yn yl Keton es
2
BMS
yield ee
entry ketone (equiv) (equiv) T (°C) alcohol 3 (%) (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1a
1a
2.0
2.0
2.0
2.0
1.0
2.0
2.0
1.0
1.0
1.0
0.5
0.5
2.0
2.0
2.0
2.0
2.0
2.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
1.1
5.0
5.0
5.0
5.0
5.0
5.0
-20
-30
-40
-30
-30
-30
-30
0
-30
-50
-30
-30
-30
0
3a 1
3a
80
80
73
84
84
73
85
30
100
89
83
90
92
26
48
54
35
81
64
71
66
88
82
88
94
74
92
86
86
84
96
86
86
95
86
98
1a
3a
1b10
1c
3b11
3c12
3c
1c
1d 13
1e15
1e
3d 14
3e
3e
3e
3e
3e
1e
1e
1e
ester of alcohol 3f shows the signals for both methoxyl
and acetylenic peaks of the major diastereomer (3.60 and
2.53 ppm) downfield of the corresponding signals for the
minor diastereomer (3.55 and 2.50 ppm). The same
chemical shift relationships were observed for the (S)-
Mosher esters of the major and minor enantiomers of
3g.21
1e
3e
1f16
1f
3f17
3f
-10
-30
0
1f
3f
1g18
1g
3g18
3g
-30
The major enantiomer of alcohol 3f was assigned the
S-configuration by comparison of the optical rotation of
The data also show that the selectivity of the reduction
improved when the size of the alkyl group increased. For
example, the reduction of alkynyl ketone 1a (R′ ) methyl)
at -30 °C with 2 mol of oxazaborolidine 2 and 5 mol of
BMS per mole of substrate gave 3a with 71% ee (entry
2, Table 1). Under the same conditions, the sterically
more hindered ketone 1b (R′ ) ethyl) provided the
corresponding alcohol 3b with an 88% ee and ketone 1e
(R′ ) cyclohexyl) provided alcohol 3e with a 96% ee
(entries 4 and 13, respectively, Table 1).
The terminal alkynyl ketones 1f and 1g were reduced
more rapidly (<20 min) than the phenylalkynyl ketones
1a -e, giving equally satisfactory results (Scheme 1,
Table 1). Again, the size of the alkyl group appears to
influence the selectivity of the reaction. For example,
reduction of ketone 1f at -30 °C provided alcohol 3f in
54% yield with 95% ee (entry 16, Table 1); under the
same conditions the sterically more hindered ketone 1g
afforded propargyl alcohol 3g in 81% yield with 98% ee
(entry 18, Table 1).
our sample with the literature value, [R]20 ) -3.9°
D
(CHCl3).17b The optical rotation of alcohol 3f (prepared
under the conditions indicated in entry 16, Table 1) was
[R]25D ) -3.4° (CHCl3). The enantiomeric excess for this
1
sample as determined from the H NMR of the Mosher
ester was 90%. We therefore assign the absolute config-
uration of all chiral alcohols (3a -g) obtained in this study
as S and we conclude that reduction of alkynyl ketones
with BMS in the presence of oxazaborolidine 2 provides
the corresponding propargyl alcohols with the S-config-
uration.
The observed enantiomeric assignments are consistent
with the general mechanistic picture originally proposed
by Corey.5a It appears that the alkynyl substituent
adopts the position of the sterically smaller RS and the
bulkier group occupies the RL position (Figure 1) for the
proposed transition state assembly (5).
Syn th esis of a Mod el Ch ir a l Diyn ed iol. Because
we are particularly interested in the synthesis of chiral
diynediols, we examined the reduction of diynedione 7.
This substrate was readily obtained by addition of 2.2
mol equiv of bis(trimethylsilyl)acetylene to glutaroyl
dichloride (6) in the presence of aluminum chloride and
desilylation of the crude double acylation product (86%,
Scheme 4).
Reduction of diynedione 7 at -30 °C with 5 mol of BMS
and 1 mol of oxazaborolidine 2 per mole of dione provided
a mixture of diastereomeric diols 8 in 84% yield. The
ratio of diasteriomers was determined by analysis of the
Assign m en t of Con figu r a tion of Ch ir a l P r op a r gyl
Alcoh ols. Comparison of the 1H NMR spectra of the (R)-
Mosher esters19 of alcohols 3a -g suggested that the
predominant component of each belonged to a single
diastereomeric series. For each sample, the major dias-
tereomer exhibited the higher field methoxyl signal (3.55
vs 3.60 ppm).20
Additional correlations could be made for the Mosher
esters of the terminal propargyl alcohols. The (S)-Mosher
(9) Dale, J . A; Mosher, H. S. J . Am. Chem. Soc. 1973, 95, 512.
(10) Hauptmann, H.; Mader, M. Tetrahedron Lett. 1977, 3151.
(11) Duranti, E.; Balsamini, C.; Spadoni, G.; Staccioli, L. J . Org.
Chem. 1988, 53, 2870.
(12) Daeuble, J . F.; McGettigan, C.; Stryker, J . M. Tetrahedron Lett.
1990, 31, 2397.

3216 J . Org. Chem., Vol. 61, No. 9, 1996
Notes
configuration. No (S)-Mosher ester product derived from
(R,R)-diol 8 was detected.
As expected, the selectivity of the reduction improved
when an excess of oxazaborolidine 2 was used. When
diynedione 7 was reduced with 3 mol of oxazaborolidine
2 per mole of doine, diols 8 were obtained in 67% yield
with a 66% de (83% ee per carbonyl reduced) of the S,S-
product.
Con clu sion
In this study we have shown the general applicability
of chiral oxazaborolidine 2 to the reduction of alkynyl
ketones. The short reaction times and low temperatures
required for reduction make this procedure an attractive
alternative to existing methodology, especially when
longer reaction times are problematic. Therefore, the
methodology described above represents a useful addition
to the tools of asymmetric synthesis.
Exp er im en ta l Section
F igu r e 2.
Gen er a l. Melting points are uncorrected. High-resolution
mass spectra were obtained under electron impact (EI), chemical
ionization (CI), or fast atom bombardment (FAB) conditions.
Thin layer chromatography (TLC) was carried out on precoated
silica gel 60F 250 plates. Preparative thin layer chromatography
was performed on precoated silica gel plates (1000 mm). Flash
column chromatography was performed with silica gel 60 (230-
400 mesh). THF was distilled from sodium benzophenone ketyl.
Methylene chloride was distilled from CaH2. Toluene was dried
over 4 Å molecular sieves.
1H NMR spectra of the Mosher diesters of the product
mixture. The (S)-Mosher diesters exhibited three dou-
blets in the region corresponding to signals for acetylenic
protons: a small signal at 2.55 ppm, a large signal at
2.53 ppm, and a second small signal (equal in intensity
to the first signal) at 2.48 ppm (Figure 2).
This pattern was consistent with a mixture of Mosher
esters in which the major product is derived from the
(S,S)-diol and the minor product from the (R,S)-diol if
and only if the Mosher ester of the (R,S)-diol gives two
signals, neither of which coincides with that of the (S)-
Mosher ester of the (S,S)-diol. In order to verify this
premise, we prepared the (S)-Mosher diester of a sample
of diols 8 which had been prepared by a nonstereoselec-
tive process.22 This sample showed four doublets of
approximately equal intensity in the acetylenic proton
region: at 2.55, 2.53, 2.50, and 2.48 ppm. We conclude
then that, in the (S)-Mosher esters of diols 8, the signals
at 2.53 represent the ester of the (S,S)-diol, that at 2.50
ppm the ester of the (R,R)-diol, and those at 2.55 and
2.48 the two diastereomeric centers in the (R,S)-diol.
Our chiral reduction then afforded a major diol with
S,S-configuration in 54% de (77% ee per carbonyl re-
duced). The minor product diol was assigned the R,S-
Gen er a l P r oced u r e for t h e P r ep a r a t ion of Alk yn yl
Keton es. The procedure described for 1e was also applied for
the syntheses of 1b-d .
1-Cycloh exyl-3-p h en yl-2-p r op yn -1-on e (1e). To a solution
of 476 mg (4.66 mmol) of phenylacetylene in 5 mL of dry THF
at 0 °C was added 2.91 mL (4.66 mmol) of n-BuLi (1.6 M in
hexane). After 15 min, 0.57 mL (52 mg, 4.7 mmol) of cyclohex-
anecarboxaldehyde was added dropwise over 2 min. After being
stirred for 30 min, the reaction was quenched with 1 mL of
methanol and diluted with 20 mL of ether. The solution was
washed with 1 M HCl (2 × 20 mL) followed by water, 5%
NaHCO3 (2 × 20 mL), and brine (2 × 20 mL). The organic layer
was dried over Na2SO4 and filtered through a thin bed of silica
gel. Evaporation of the solvent gave an orange oil. This crude
material was dissolved in 15 mL of CCl4. After addition of two
scoops of powdered 4 Å molecular sieves, the reaction mixture
was aged for 30 min. Then, 7.31 g (84.1 mmol) of MnO2 was
added. After 20 min the black slurry was filtered through a glass
fritt and washed through with two 10 mL portions of CCl4.
Evaporation of the solvent followed by bulb-to-bulb vacuum
distillation afforded 762 mg (77% overall) of ketone 1e as a pale
yellow oil. In some cases, a portion of the ketone was further
purified just prior to reduction by preparative thin layer chro-
matography (1:4 ethyl ether:hexanes).
1-P h en yl-1-p en tyn -3-on e (1b). Phenylacetylene (527 mg,
5.16 mmol), BuLi (3.23 mL, 5.2 mmol), propionaldehyde (0.37
mL, 5.2 mmol), and MnO2 (8.2 g, 94 mmol) afforded 446 mg
(55%).
1-P h en yl-1-n on yn -3-on e (1c). Phenylacetylene (899 mg,
8.80 mmol), BuLi (5.50 mL, 8.8 mmol), heptanal (1.23 mL, 8.80
mmol), and MnO2 (11.5 g, 132 mmol) afforded 1.08 g (58%): IR
(neat) 3061, 2929, 2201, 1672 cm-1; 1H NMR (CDCl3) δ 7.57 (m,
2 H), 7.42 (m, 3 H), 2.65 (t, J ) 7.4 Hz, 2 H), 1.75 (m, 2 H), 1.34
(m, 6 H), 0.90 (t, J ) 6.2 Hz, 3 H); 13C NMR (CHCl3) δ 188.3,
133.0, 130.6, 120.1, 90.5, 87.8, 45.5, 31.5, 28.6, 24.1, 22.4, 14.0;
HRMS (MH+) calcd 215.1436, found 215.1432.
(13) Tohda, Y.; Sonogashira, K; Hagihara, N. Synthesis 1977, 777.
(14) Kuwajima, I.; Nakamura, E.; Hashimoto, K. Tetrahedron 1983,
39, 975.
(15) Nahm, S.; Weinreb, S. M. Tetrahedron Lett. 1981, 22, 3815.
(16) Chabaud, B.; Sharpless, K. B. J . Org. Chem. 1979, 44, 4202.
(17) The chiroptical properties for this compound have been studied,
and the optical rotation has been correlated to absolute stereochem-
istry. (a) Dorta de Marquez, M.; Rowland, P. J .; Scopes, P. M.; Thaller,
V. J . Chem. Res., Miniprint 1986, 1348. (b) Glanzer, B. I.; Faber, K.;
Griengl, H. Tetrahedron 1987, 43, 5791.
(18) Kluge, A. F.; Kertesz, D. J .; O-Yang, C.; Wu, H. Y. J . Org. Chem.
1987, 52, 2860.
(19) “(R)-Mosher ester” refers to esters prepared from the (S)-Mosher
acid chloride; likewise, “(S)-Mosher ester” refers to esters prepared from
the (R)-Mosher acid chloride.
(20) Conversely, in the 1H NMR spectra of the (S)-Mosher esters,
the methoxyl peak for the major diastereomer appears downfield of
the methoxyl peak for the minor diastereomer.
(21) As expected, the 1H NMR spectrum of the (R)-Mosher ester of
alcohol 3g shows both the methoxyl and acetylenic hydrogen peaks
for the major diastereomer to be upfield of those for the minor
diastereomer.
4-Meth yl-1-p h en yl-1-p en tyn -3-on e (1d ). Phenylacetylene
(542 mg, 5.32 mmol), BuLi (3.33 mL, 5.3 mmol), isobutyralde-
hyde (0.38 mL, 5.3 mmol), and MnO2 (8.4 g, 96 mmol) afforded
367 mg (39%).
Gen er a l P r oced u r e for th e P r ep a r a tion of Ter m in a l
Alk yn yl Keton es. The procedure described for 6 was also
applied for the syntheses of 1f and 1g.
(22) The stereo-random sample of diols 8 was obtained in 99% yield
(983 mg, 6.47 mmol) by treatment of glutaric dialdehyde (653 mg) with
an excess of ethynylmagnesium bromide (52 mL, 0.5 M in THF) in
THF at ambient temperature.

Notes
1,8-Non a d iyn e-3,7-d ion e (6). To a stirred solution of 1.81
J . Org. Chem., Vol. 61, No. 9, 1996 3217
THF. The solution was cooled to -30 °C. Then, 0.16 mL (1.6
mmol, ∼10 M) of boron methyl sulfide complex was added over
5-10 min. Reaction progress was monitored by TLC (small
aliquots were diluted with ether and quenched with 1 M HCl).
After the reaction appeared to be complete, it was quenched by
slow dropwise addition of 1.0 mL of methanol. The solution was
diluted with 20 mL of ether and washed with saturated NH4+Cl-
(2 × 10 mL), 5% NaHCO3 (2 × 10 mL), and brine (2 × 10 mL).
The organic layer was dried over MgSO4, filtered through silica
gel, and concentrated. Column chromatography (10% ethyl
acetate in hexanes) afforded 36 mg (0.26 mmol, 81%) of a
colorless crystalline solid: mp 49-50 °C.
(S)-1-Cycloh exyl-3-p h en yl-2-p r op yn -1-ol (3e): IR (neat)
3340 (b), 2925, 2852, 2230, 1598, 1490 cm-1; 1H NMR (CDCl3) δ
7.45 (m, 2 H), 7.32 (m, 3 H), 4.39 (d, J ) 5.9 Hz, 1 H), 2.05 (m,
1 H), 1.93 (m, 2 H), 1.78 (m, 2); 13C NMR (CDCl3) δ 131.7, 128.3,
128.2, 122.7, 89.2, 85.6, 67.7, 44.3, 28.6, 28.2, 26.4, 25.9, 25.88;
HRMS calcd 214.1357, found 214.1355.
g (10.7 mmol) of glutaroyl dichloride and 5.3 mL (4.0 g, 24 mmol)
of bis(trimethylsilyl)acetylene in 50 mL of dry CH2Cl2 at 0 °C
was added 3.3 g (25 mmol) of AlCl3. After 2.5 h, the mixture
was poured into 100 mL of ice-water. The layers were
separated, and the aqueous layer was extracted with CH2Cl2 (2
× 25 mL). The combined organic layer was washed with 5%
NaHCO3 (4 × 25 mL) and dried over MgSO4. Filtration through
silica gel followed by evaporation of the solvent and bulb to bulb
vacuum distillation provided 2.97 g of a crude yellow oil (95%
yield). This material (504 mg) was dissolved in 15 mL of
methanol, and 2 mL of water and a catalytic amount of borax
were added to the stirred solution. After 0.5 h the reaction was
complete (TLC). The mixture was diluted with 40 mL of 1%
citric acid and extracted with ethyl acetate (3 × 25 mL). The
organic layer was washed with 40 mL of brine, dried over Na2-
SO4, and filtered. Evaporation of the solvent provided 237 mg
of an orange oil. Flash chromatography (10% ethyl acetate in
hexanes) afforded 214 mg (1.56 mmol, 89% yield overall) of dione
1,8-Non a d iyn e-3,7-d iol (8): IR (neat) 3290, 2949, 2868, 2114
cm-1; 1H NMR (CDCl3) δ 4.41 (m, 2 H), 2.48 (d, J ) 2.1 Hz, 2H),
1.79 (m, 6 H); 13C NMR (CDCl3) δ 84.63, 73.14, 62.09, 37.03,
20.62, 20.59; HRMS calcd (MH+) 159.0916, found 159.0913.
6 as a colorless oil: IR (neat) 3261, 2941, 2899, 2093, 1680 cm-1
;
1H NMR (CDCl3) δ 3.24 (s, 2 H) 2.68 (t, J ) 3.1 Hz, 4 H), 2.03
(m, 2 H); 13C NMR (CHCl3) δ 186.0, 81.1, 78.9, 43.8, 17.3; HRMS
calcd 148.0524, found 148.0520.
Ack n ow led gm en t. Financial support from the Pe-
troleum Research Fund (Grant No. 24010-AC, admin-
istered by the American Chemical Society) and from the
National Science Foundation (Grant No. CHE-95-21055)
is gratefully acknowledged.
1-Decyn -3-on e (1f). Octanoyl chloride (624 mg, 3.83 mmol),
bis(trimethylsilyl)acetylene (0.95 mL, 4.2 mmol), AlCl3 (560 mg,
4.21 mmol), and borax (93 mg, 0.38 mmol) afforded 458 mg
(79%).
1-Cycloh exyl-2-p r op yn -1-on e (1g). Cyclohexylcarboxylic
acid chloride (708 mg, 4.83 mmol), bis(trimethylsilyl)acetylene
(1.20 mL, 5.31 mmol), AlCl3 (706 mg, 5.31 mmol), and borax (110
mg, 0.45 mmol) afforded 450 mg (73%).
Gen er a l P r oced u r e for t h e Syn t h esis of P r op a r gyl
Alcoh ols. The procedure described for the preparation of 3g
was applied, as modified in Table 1, for the syntheses of alcohols
3a -f and diols 8. For yield and enantiomeric excesses, refer to
Table 1.
(S)-1-Cycloh exyl-2-p r op yn -1-ol (3g). A solution of 44 mg
(0.32 mmol) of ketone 1g in 1.5 mL of THF was dried over 4 Å
molecular sieves for 2 h and subsequently added by syringe to
a dry flask charged with 0.65 mmol of reagent 2 and 1.5 mL of
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
and IR spectra for 1-phenyl-1-nonyn-3-one (1c), 1-cyclohexyl-
3-phenyl-2-propyn-1-ol (3e), 1,8-nonadiyne-3,7-dione (6), and
1,8-nonadiyne-3,7-diols (8) are provided. 1H NMR spectra of
the Mosher esters derived from alcohols 3f,g and 8 are also
provided (21 pages). This material is contained in libraries
on microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
J O951712O