Syntheses of new C2-symmetric, optically active 1,2-diols bearing tertiary alkyl groups

Article abstract of DOI:10.1016/S0957-4166(99)00325-0

New C₂-symmetric chiral 1,2-diols, 1,2-bis(1-adamantyl)-1,2-ethanediol and 3,3,6,6-tetramethyl-1,2-cyclohexanediol, were synthesized by the use of a new resolution method.

Full text of DOI:10.1016/S0957-4166(99)00325-0

Pergamon
Tetrahedron: Asymmetry 10 (1999) 3209–3218
Syntheses of new C2-symmetric, optically active 1,2-diols
bearing tertiary alkyl groups
Tadahiro Takeda and Tsuneo Imamoto ∗
Department of Chemistry, Faculty of Science, Chiba University, Inage, Chiba 263-8522, Japan
Received 1 July 1999; accepted 30 July 1999
Abstract
New C2-symmetric chiral 1,2-diols, 1,2-bis(1-adamantyl)-1,2-ethanediol and 3,3,6,6-tetramethyl-1,2-
cyclohexanediol, were synthesized by the use of a new resolution method. © 1999 Elsevier Science Ltd. All rights
reserved.
1. Introduction
Optically active 1,2-diols play important roles as chiral auxiliaries and ligands in asymmetric
syntheses,1 and a number of diols of this class have been reported so far.2 Among them, the 1,2-diols
bearing tertiary alkyl groups at the stereogenic centers have been rarely described, despite the potentially
high utility.3 Previously the enantiomerically pure 2,2,5,5-tetramethyl-3,4-hexanediol 1 was prepared,
and we demonstrated that it exhibited high enantioselectivity in catalytic asymmetric oxidations of
sulfides.4 We considered that this selectivity might be due to a steric contrast between the tert-butyl
group and the hydrogen atom at the stereogenic center. This consideration has led us to explore 1,2-bis-
(1-adamantyl)-1,2-ethanediol 2 and 3,3,6,6-tetramethyl-1,2-cyclohexanediol 3, which might create more
effective asymmetric environments owing to the bulkier alkyl groups or more rigid structure. In this paper
we report the syntheses of these compounds together with a new resolution method.
∗
Corresponding author. Tel: +81-43-290-2791; fax: +81-43-290-2791; e-mail: imamoto@scichem.s.chiba-u.ac.jp
0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00325-0

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2. Results and discussion
2.1. Synthesis of optically active 1,2-bis(1-adamantyl)-1,2-ethanediol
Optically active 1,2-bis(1-adamantyl)-1,2-ethanediol 2 was synthesized according to the reaction
sequences shown in Scheme 1. The protection of acyloin 45 as the trimethylsilyl ether, followed by
the reduction of the carbonyl group with LiAlH4, produced the key intermediate (ꢀ)-2 in good yield and
with high stereoselectivity.6 The racemic diol 2 was transformed into the cyclic phosphates possessing
a l-menthyl group.4,7 The resulting diastereomer mixture was separated by recycling preparative HPLC
to give colorless needles (mp 105–107°C) and colorless prisms (mp 187–189°C), respectively. In order
to determine the absolute configurations of these diastereomers, the molecular structure of the latter
crystal was analyzed by X-ray crystallography. The ORTEP drawing is shown in Fig. 1, which apparently
indicates that the compound possesses the (R,R) configuration. This diastereomer 7 was treated with MeLi
to give (−)-2. In a similar manner, (+)-2 was also prepared from the other diastereomer 6.8
Scheme 1.
2.2. Synthesis of enantiomerically pure 3,3,6,6-tetramethyl-1,2-cyclohexanediol
Synthesis of cis- and trans-3,3,6,6-tetramethyl-1,2-cyclohexanediol 3 was reported by Applequist and
co-workers,9 but their synthetic route gave the cis-diol as a major product. Therefore, we devised an
alternative route to diol 3 (Scheme 2). The dimethylester 910 was subjected to intramolecular acyloin
condensation by sodium metal,11 followed by reduction with sodium metal in the presence of 2-
propanol,12 to give trans-diol 3 in 52% yield.13 It should be noted that these reaction sequences were
carried out in one pot, and that only trace amounts of undesired cis-diol were produced.
The observed high stereoselectivity can be explained by considering the stable conformation of the
intermediate A (Fig. 2). The two oxygen atoms occupy the equatorial positions to avoid the 1,3-diaxial

T. Takeda, T. Imamoto / Tetrahedron: Asymmetry 10 (1999) 3209–3218
3211
Figure 1. ORTEP drawing of compound 7
Scheme 2.
Figure 2.
interactions. The lone pair at the axial position as well as the oxygen anions abstracts protons to form the
trans-diol.14,15
The resolution of (ꢀ)-trans-diol 3 was attempted by the methods used for the diol 1 or 2,4 but the
desired products were not obtained. After the various attempts at resolution, we found that efficient
resolution was achieved by converting trans-diol 3 into the amino acid ester (Scheme 3). Thus, (ꢀ)-trans-
diol 3 and N-benzoyl l-proline 10 were treated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hy-
drochloride (EDC-HCl) to give a mixture of two diastereomeric amino acid esters in quantitative yield.16
Diastereomerically pure 11 was isolated by recrystallization of the mixture from cyclohexane:EtOAc

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T. Takeda, T. Imamoto / Tetrahedron: Asymmetry 10 (1999) 3209–3218
(5:1). Enantiomerically pure (+)-3 was furnished by the subsequent hydrolysis of this diastereomer in
39% yield from (ꢀ)-trans-diol 3. Unfortunately, the other diastereomer was not obtained as a good
crystalline solid.
Scheme 3.
The absolute configuration of diol (+)-3 was unequivocally determined as (S,S) on the basis of X-ray
structural analysis of amino acid ester 11 (Fig. 3). The ORTEP drawing apparently indicates the existence
of the hydrogen bond between O(1) and O(4). We consider that this hydrogen bond may serve for the
formation of the rigid structure, which may be one of the factors of easy crystallization.
Figure 3. ORTEP drawing of compound 11. Distance of O(1)–O(4): 2.841(5) Å

T. Takeda, T. Imamoto / Tetrahedron: Asymmetry 10 (1999) 3209–3218
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2.3. Catalytic asymmetric oxidation of sulfides
To test the catalytic efficiency of diols 2 and 3, the asymmetric oxidation of sulfides using Ti(IV)–diol
complex was examined (Scheme 4).4,17 Under the same conditions as the reaction using diol 1, the re-
actions proceeded sluggishly to produce the corresponding sulfoxides with quite low enantioselectivities
(Table 1). These low selectivities may be attributed to the formation of the non-effective Ti(IV)–diol
complexes.
Scheme 4.
Table 1
Catalytic asymmetric oxidation of sulfides
3. Conclusion
We have synthesized two new optically active 1,2-diols, and developed a new method for their
resolution via amino acid esters. Further studies directed towards application of these diols in various
asymmetric reactions are under way.
4. Experimental
4.1. General procedure
All melting points were measured on Yamato micro melting point apparatus and were uncorrected.
Optical rotations were measured with JASCO DIP-370 polarimeter. IR spectra were performed with a
Hitachi IR 215 spectrophotometer. NMR spectra were measured with JEOL JMN-LA-400 (400 MHz)
spectrometer in CDCl3. Chemical shifts were reported by δ ppm. HRMS (FAB) spectra were measured
with JEOL HX-110 spectrometer in Chemical Analysis Center, Chiba University. Organic solvents used

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T. Takeda, T. Imamoto / Tetrahedron: Asymmetry 10 (1999) 3209–3218
were dried by standard methods. Commercially available reagents were used without further purification.
Silica gel (Wakogel, C-200) was used for column chromatography. HPLC analyses were performed on a
Hitachi L-6000 pump, L-7490 RI detector, and L-4000 UV detector with an appropriate chiral column.
Recycling preparative HPLC was performed on JAIGEL-ODS 345-15 column, JAI LC-908 pump and RI
detector RI-5.
4.2. 1,2-Bis(1-adamantyl)-2-(trimethylsilyl)oxyethanone 5
To a solution of 1,2-bis(1-adamantyl)-2-hydroxyethanone 4 (37 g, 0.11 mol) and 4-(N,N-
dimethylamino)pyridine (1.2 g, 0.01 mol) in pyridine was added TMSCl (43.1 mL, 0.34 mol) at
rt under Ar atmosphere. After the mixture was stirred for 2 h, the reaction was quenched with water.
The organic layer was separated, and the aqueous layer was extracted with Et2O three times. The
combined extracts were washed with brine and dried (Na2SO4). The solvent was evaporated under
reduced pressure, and washed with hexane to give 5 (43 g, 96%) as a white powder: mp 132–134°C; IR
1
(KBr) 2905, 2850, 1705, 1450, 1250, 1100, 880, 835 cm−1; H NMR (400 MHz, CDCl3) δ 0.16 (9H,
s), 1.22–2.05 (30H, m), 4.16 (1H, s); 13C NMR (100 MHz, CDCl3) δ 1.03, 27.7, 28.0, 28.3, 36.4, 36.5,
37.0, 37.6, 37.8, 38.4, 38.5, 38.8, 46.9, 214.9; FAB MS m/z 401 (M++1H); HRMS calcd for C25H41O2Si
(M++1H) 401.2876, found 401.2871.
4.3. (ꢀ)-1,2-Bis(1-adamantyl)-1,2-ethanediol 2
To the suspension of lithium aluminum hydride (4.1 g, 0.11 mol) in THF was slowly added a solution
of 5 (43 g, 0.11 mol) in THF at rt under Ar atmosphere, and the mixture was refluxed for 5 h. The reaction
mixture was carefully poured into concentrated HCl at 0°C. After the mixture was diluted with water, the
organic layer was separated, and the aqueous layer was extracted with Et2O three times. The combined
extracts were washed with saturated aqueous NaHCO3 and brine, and dried (Na2SO4). The solvent was
evaporated under reduced pressure, and the residue was recrystallized from DME to give 2 (22.4 g, 61%)
as colorless needles: mp 277–279°C; IR (KBr) 3400, 2900, 2850, 1450, 1080, 605 cm−1; 1H NMR (400
MHz, CDCl3) δ 1.51–1.73 (30H, m), 2.25 (2H, d, J=6.8 Hz), 3.20 (2H, d, J=6.5 Hz); 13C NMR (100
MHz, CDCl3) δ 28.2, 36.7, 37.2, 38.0, 74.0; FAB MS m/z 331 (M++1H). Anal. calcd for C22H34O2: C,
9.95; H, 10.37. Found: C, 80.17; H, 10.58.
4.4. Preparation of diastereomerically pure phosphates 6 and 7
To a solution of (ꢀ)-2 (4.7 g, 14 mmol) in THF was added n-BuLi (18.2 mL of 1.54 M hexane
solution, 28 mmol) at 0°C under Ar atmosphere. The mixture was added to a solution of dichloro(l-
menthyloxy)phosphine (3.8 g, 14 mmol) in THF at −78°C, and the reaction mixture was allowed to
warm to rt. The reaction was quenched with water. The organic layer was separated, and the aqueous
layer was extracted with ethyl acetate three times. The combined extracts were washed with brine and
dried (Na2SO4). The solvent was evaporated under reduced pressure, and the residue was added to H2O2
(1.6 mL of 30% water solution, 14 mmol) at rt. After the mixture was stirred for 3 h, the reaction
was quenched with saturated aqueous Na2S2O3. The mixture was extracted with hexane five times.
The combined extracts were washed with brine and dried (Na2SO4). The solvent was evaporated under
reduced pressure, and the residue was purified by chromatography on silica gel (hexane:EtOAc, 50:1)
to give 6 and 7 (5.6 g, 75%) as colorless solids. This mixture of two diastereomers was separated by

T. Takeda, T. Imamoto / Tetrahedron: Asymmetry 10 (1999) 3209–3218
3215
recycling HPLC (MeOH). The compounds 6 (1.6 g, 29%) and 7 (1.5 g, 27%) were obtained from the first
and second fraction, respectively.
4.5. (10S,20S)-(10,20-Diadamantyl-10,20-ethanediyl) l-menthyl phosphate 6
Colorless needles: mp 105–107°C; [α]21 −64.2 (c 1.02, CHCl3); IR (KBr) 2900, 2860, 1450, 1280,
D
1
1060, 1030, 985, 960, 870 cm−1; H NMR (400 MHz, CDCl3) δ 0.83–2.28 (48H, m), 3.91 (1H, dd,
J=18.5, 3.1 Hz), 3.95 (1H, dd, J=17.3, 3.1 Hz), 4.25–4.35 (1H, m); 13C NMR (100 MHz, CDCl3) δ 16.1,
20.8, 22.0, 23.2, 25.9, 27.8 (d, J=16.4 Hz), 31.5, 34.1, 36.4 (d, J=4.9 Hz), 36.8 (d, J=11.5 Hz), 37.2 (d,
J=16.4 Hz), 42.8, 48.3 (d, J=8.2 Hz), 80.4 (d, J=6.6 Hz), 84.8 (d, J=2.5 Hz), 85.1 (d, J=1.6 Hz); FAB
MS m/z 529 (M+−1H); HRMS calcd for C32H52O4P (M++1H) 531.3603, found 531.3600.
4.6. (10R,20R)-(10,20-Diadamantyl-10,20-ethanediyl) l-menthyl phosphate 7
Colorless prisms: mp 187–189°C; [α]21 +12.5 (c 1.01, CHCl3); IR (KBr) 2900, 2860, 1450, 1280,
D
1
1060, 1030, 985, 960, 870 cm−1; H NMR (400 MHz, CDCl3) δ 0.83–2.25 (48H, m), 3.91 (1H, dd,
J=11.4, 2.9 Hz), 3.92 (1H, dd, J=9.9, 2.9 Hz), 4.30–4.39 (1H, m); 13C NMR (100 MHz, CDCl3) δ
15.9, 20.9, 21.9, 23.0, 26.3, 27.8, 31.5, 34.1, 36.4 (d, J=4.9 Hz), 36.8 (d, J=5.7 Hz), 37.2 (d, J=3.3 Hz),
42.9, 48.3 (d, J=6.6 Hz), 81.0 (d, J=7.4 Hz), 84.9 (d, J=1.6 Hz), 85.1 (d, J=2.5 Hz); FAB MS m/z 529
(M+−1H); HRMS calcd for C32H52O4P (M++1H) 531.3603, found 531.3617.
4.7. X-Ray crystallographic analysis of compound 7
A well-shaped monoclinic crystal of 7 was obtained by recrystallization from Et2O: C32H51O4P;
space group P21 (#4); a=10.877(7) Å, b=12.474(8) Å, c=12.474(8) Å; V=1507(1) Å3; Z=2, D=1.169
g/cm3; F(000)=580; µ(Mo Kα)=1.25 cm−1; λ(Mo Kα)=0.71070 Å; temperature of data collection 300 K;
2669 reflections measured, 2603 observed (I >3.00σ(I)); 335 variables; R=0.055, RW=0.080, GOF=1.36.
Selected bond distance (Å) and angles (deg): P(1)–O(1) 1.584(3), P(1)–O(2) 1.589(3), P(1)–O(3)
1.562(3), P(1)–O(4) 1.462(3), O(1)–P(1)–O(2) 97.6(1), O(1)–P(1)–O(3) 104.6(2), O(1)–P(1)–O(4)
117.4(2), O(2)–P(1)–O(3) 105.4(2), O(2)–P(1)–O(4) 116.1(4), O(3)–P(1)–O(4) 113.7(1).
4.8. (1S,2S) and (1R,2R)-1,2-Bis(1-adamantyl)-1,2-ethanediol 2
Diastereomerically pure 6 (0.82 g, 1.6 mmol) in toluene was treated with MeLi (5.3 mL of 1.5 M
Et2O solution, 8 mmol) at rt under Ar atmosphere, and the mixture was stirred for 5 h. The reaction
mixture was poured into vigorously stirred water. The organic layer was separated, and the aqueous layer
was extracted with ethyl acetate three times. The combined extracts were washed with brine and dried
(Na2SO4). The solvent was evaporated under reduced pressure. The residue was purified by flash column
chromatography (hexane:EtOAc, 15:1), and recrystallized from DME to give optically active (1S,2S)-2
(185 mg, 35%) as colorless needles: mp 270–272°C; [α]25 +14.5 (c 0.77, CHCl3).
D
In a similar manner, optically active (1R,2R)-2 was obtained from 7 (195 mg, 37%): mp 271–273°C;
[α]25 −13.7 (c 1.01, CHCl3).
D

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4.9. Dimethyl 2,2,5,5-tetramethylhexanedioate 9
To a solution of 2,2,5,5-tetramethylhexanedioic acid 8 (17.7 g, 88 mmol) and KOH (11.8 g, 210 mmol)
in MeOH was added iodomethane (20 mL, 320 mmol) at rt, and the mixture was refluxed for 3 h. The
reaction was quenched with water, and the mixture was extracted with Et2O three times. The combined
extracts were washed with brine and dried (Na2SO4). The solvent was evaporated under reduced pressure,
and the residue was purified by chromatography on silica gel (hexane) to give 918 (12.6 g, 61%) as a
colorless solid: mp 35–36°C; 1H NMR (400 MHz, CDCl3) δ 1.16 (12H, s), 1.44 (4H, s), 3.66 (6H, s);
13C NMR (100 MHz, CDCl3) δ 25.0, 35.6, 42.0, 51.6, 178.2.
4.10. trans-3,3,6,6-Tetramethyl-1,2-cyclohexanediol 3
Metallic sodium (7.4 g, 0.32 mol) in xylene was refluxed until the sodium melted under Ar atmosphere.
The oil bath was removed and the mixture was cooled to rt with very vigorous stirring. The solvent was
removed with a syringe, and to the powdered sodium was added the solution of diester 9 (4.6 g, 0.02
mol) in Et2O. The mixture was refluxed for 3 days, and then slowly added 2-propanol (25 mL, 0.32 mol).
After additional reflux for 2 h, the reaction was quenched with water. The organic layer was separated,
and the aqueous layer was extracted with Et2O three times. The combined extracts were washed with 1
M HCl, saturated aqueous NaHCO3 and brine, and dried (Na2SO4). The solvent was evaporated under
reduced pressure. The residue was purified by chromatography on silica gel (hexane:EtOAc 5:1), and
1
recrystallized from n-Bu2O to give racemic 3 (1.8 g, 52%) as colorless needles: mp 150–152°C; H
NMR (400 MHz, CDCl3) δ 0.89 (6H, s), 1.01 (6H, s), 1.34 (4H, dd, J=83.4, 9.7 Hz), 2.51 (2H, s), 3.22
(2H, s); 13C NMR (100 MHz, CDCl3) δ 18.4 (d, 4.1 Hz), 29.5 (d, 4.1 Hz), 34.6, 36.3, 78.0.
4.11. (10S,20S)-(20-Hydroxy-30,30,60,60-tetramethyl)cyclohexyl (S)-1-benzoyl-2-pyrrolidine-carboxylate
11
To a solution of racemic 3 (0.34 g, 2 mmol), N-benzoyl l-proline 10 (0.53 g, 2.4 mmol) and 4-
(N,N-dimethylamino)pyridine (0.12 g, 1 mmol) in CH2Cl2 was added EDC-HCl (0.7 g, 3.6 mmol)
and Et3N (0.5 mL, 3.6 mmol) at rt under Ar atmosphere, and the mixture was stirred for 2 h. The
reaction was quenched with 1 M HCl (50 mL), and the mixture was added to Et2O (50 mL). The
organic layer was separated, and the aqueous layer was extracted with Et2O three times. The combined
extracts were washed with saturated aqueous NaHCO3 twice and brine, and dried (Na2SO4). The solvent
was evaporated under reduced pressure, and the residue was dried in vacuo to give the mixture of
diastereomers (0.75 g, 100%). The mixture was recrystallized from cyclohexane–EtOAc to give amino
acid ester 11 (0.29 g, 39%) as colorless plates: mp 171°C (dec.); [α]20 −3.47 (c 0.99, CHCl3); IR (KBr)
D
3450, 2930, 1735, 1620, 1600, 1580, 1455, 1300, 1085, 1045, 980, 800, 740, 705 cm−1; 1H NMR (400
MHz, CDCl3) δ 0.92 (3H, s), 0.94 (3H, s), 0.97 (3H, s), 1.04 (3H, s), 1.23–1.30 (2H, m), 1.45 (1H, dt,
J=4.0, 14.3 Hz), 1.57 (1H, dt, J=4.9, 13.7 Hz), 1.92–2.08 (2H, m), 2.10–2.18 (1H, m), 2.38–2.47 (1H, m),
3.25–3.30 (2H, m), 3.56–3.66 (2H, m), 4.68 (1H, dd, J=8.5, 4.9 Hz), 4.84 (1H, d, J=9.5 Hz), 7.40–7.47
(3H, m), 7.51–7.54 (2H, m); 13C NMR (100 MHz, CDCl3) δ 18.6, 19.8, 25.4, 29.3, 29.6, 29.8, 34.7,
36.3, 36.8, 50.3, 60.1, 75.7, 81.6, 127.0, 128.5, 130.4, 136.1, 170.6, 171.6; FAB MS m/z 374 (M++1H).
Anal. calcd for C22H31NO4: C, 70.75; H, 8.37; N, 3.75. Found: C, 70.84; H, 8.52; N, 3.84.

T. Takeda, T. Imamoto / Tetrahedron: Asymmetry 10 (1999) 3209–3218
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4.12. X-Ray crystallographic analysis of compound 11
A well-shaped monoclinic crystal of 11 was obtained by recrystallization from toluene: C22H31NO4;
space group P212121 (#19); a=9.158(4) Å, b=34.678(9) Å, c=6.730(4) Å; V=2137(1) Å3; Z=4, D=1.161
g/cm3; F(000)=808.00; µ(Mo Kα)=0.79 cm−1; λ(Mo Kα)=0.71070 Å; temperature of data collection
173 K; 1950 reflections measured, 1853 observed (I >1.50σ(I)); 245 variables; R=0.089, RW=0.109,
GOF=1.91. Selected distance (Å): O(1)–O(2) 2.838(5), O(1)–O(4) 2.841(5), O(2)–O(4) 2.948(4).
4.13. (1S,2S)-3,3,6,6-Tetramethyl-1,2-cyclohexanediol 3
A solution of amino acid ester 11 (0.8 g, 2.14 mmol) and KOH (14 g) in H2O (50 mL) was refluxed
for 6 h. The mixture was extracted with Et2O three times. The combined extracts were washed with 1
M HCl, saturated aqueous NaHCO3 and brine, and dried (Na2SO4). The solvent was evaporated under
reduced pressure, and the residue was dried in vacuo to give (S,S)-3 (366 mg, 100%) as colorless needles:
mp 152–153°C; [α]25 +27.2 (c 1.04, CHCl3).
D
The enantiomeric excess was determined to be 100% ee by chiral HPLC analysis: Daicel Chiralpak
AD (hexane:2-propanol 9:1, flow rate=1.0 mL/min): tr(S,S)=5.9 min, tr(R,R)=8.0 min.
4.14. Asymmetric oxidation of sulfides
The solution of Ti(OiPr)4 (7.4 µL, 0.025 mmol), MS4A (100 mg), and diol (0.05 mmol) in toluene (1
mL) was stirred for 1 h at rt, and then sulfide (0.5 mmol) was added. The solution was cooled to −20°C,
and 80% cumyl hydroperoxide (190 µL, 1 mmol) was added. The mixture was stirred at same temperature
by monitoring the reaction by TLC until sulfide disappeared. The reaction was quenched with ca.
10% aqueous solution of sodium sulfite. The aqueous layer was extracted with EtOAc three times.
The combined organic layer was washed with brine and dried (Na2SO4). The solvent was evaporated
under reduced pressure, and the residue was purified by column chromatography (EtOAc) on silica gel
to give sulfoxide. The enantiomeric excess of sulfoxide was determined by chiral HPLC analysis: Daicel
Chiralcel OD-H (hexane:2-propanol 9:1, flow rate=0.5 mL/min) for methyl p-tolyl sulfoxide, and Daicel
Chiralcel OJ (hexane:2-propanol 5:1, flow rate=0.8 mL/min) for benzyl phenyl sulfoxide.
Acknowledgements
The authors thank Dr Yoshinori Yamanoi for his helpful discussion and suggestions, and Mr Hideyuki
Tsuruta and Mr Masayoshi Nishiura for X-ray structural determinations. This work was supported by
Grants-in-Aid for Scientific Research from the Ministry of Education, Sciences, Sports and Culture,
Japan.
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11. Snell, J. M.; McElvain, S. M. Org. Synth. II 1943, 114.
12. Paquette, L. A. Encyclopedia of Reagents for Organic Synthesis; John Wiley: New York, 1995; p. 4491.
13. 3,3,6,6-Tetramethyl-2-hydroxycyclohexanone6 was isolated, and then reduced with sodium metal in the presence of 2-
propanol to give trans-diol in 70% yield.
14. Cyclic α-silyloxyketone was reduced with LiAlH4 to give cis enriched product.
15. (a) Trost, B. M.; Fleming, I. Comprehensive Organic Synthesis; Pergamon Press: Oxford, 1991; Vol. 8, p 1. (b) Fujita, M.;
Hiyama, T. J. Org. Chem. 1988, 53, 5405.
16. Amino acid 10 has been utilized for kinetic resolution of chiral alcohol, see: Chinchilla, R.; Nájera, C.; Yus, M.
Tetrahedron: Asymmetry 1990, 1, 851.
17. (a) Brunel, J. M.; Kagan, H. B. Synlett 1996, 404. (b) Brunel, J. M.; Kagan, H. B. Bull. Soc. Chim. Fr. 1996, 133, 1109. (c)
Komatsu, N.; Hashizume, M.; Sugita, T.; Uemura, S. J. Org. Chem. 1993, 58, 4529. (d) Di Furia, F.; Licini, G.; Modena,
G.; Motterle, R. J. Org. Chem. 1996, 61, 5175. (e) Superchi, S.; Rosini, C. Tetrahedron: Asymmetry 1997, 8, 349. (f)
Donnoli, M. I.; Superchi, S.; Rosini, C. J. Org. Chem. 1998, 63, 9392.
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