CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

(2R,3S,4S)-1,2-Cyclohexylidinedioxy-4-methyl-5-hexen-3-ol 69c. colourless oil; R f =
24
0.66 (20% EtOAc/hexane); [α] D +2.4 (c 1.21, CHCl3 ); IR: 3408, 1657, 997 cm -1 ; 1 H
NMR: δ 1.03 (d, J = 6.6 Hz, 3H), 1.22-1.57 (m, 10H), 1.97 (broad s, 1H), 2.32-2.42 (m,
1H), 3.56-3.59 (m, 1H), 3.82-4.07 (m, 3H), 5.05-5.12 (m, 2H), 5.74-5.91 (m, 1H); 13 C
NMR: δ 12.7, 16.4, 23.9, 25.1, 34.8, 36.2, 40.7, 65.1, 71.7, 74.8, 109.1, 115.9, 139.8.
(2R,4R)- and (2R,4S)-1,2-Cyclohexylidenedioxy-4-methyl-5-hexen-3-one 70b and 70c.
To a cooled (0 o C) and stirred suspension of PCC (1.6 g, 5.84 mmol) and NaOAc (0.3 g) in
CH 2 Cl 2 (10 mL) was added 69b and 69c (1.0 g, 4.42 mmol) in CH 2 Cl 2 (10 mL). After
stirring the reaction mixture for 3 h, it was diluted with dry Et 2 O (80 mL), and the
supernatant filtered through a pad of silica gel. The eluate was concentrated in vacuo and
the residue subjected to column chromatography (silica gel, 0-15% EtOAc/hexane) to give
70b and 70c.
70b: Yield 0.74 g (75%); colourless thick oil; IR: 1741 cm -1 ; [α] 24 D +10.2 (c 1.56, CHCl 3 );
1 H NMR: δ 1.04 (d, J = 7.6 Hz, 3H), 1.41-1.63 (m, 10H), 3.62-3.75 (m, 1H), 3.85-4.05 (m,
2H), 4.43 (dd, J = 5.8 and 7.4 Hz, 1H), 4.82-5.07 (m, 2H), 5.64-5.84 (m, 1H); 13 C NMR: δ
14.7, 23.4, 23.6, 24.7, 34.2, 35.3, 46.0, 65.5, 78.4, 110.9, 116.8, 136.2, 209.7.
70c: Yield 0.78 g (79%); colourless thick oil; [α] 24 D +5.9 (c 1.08, CHCl 3 ); IR: 1740 cm -1 ;
1 H NMR: δ 1.01 (d, J = 7.0 Hz, 3H), 1.32-1.54 (m, 10H), 3.41-3.62 (m, 1H), 3.78-3.91 (m,
1H), 3.97-4.21 (m, 1H), 4.35-4.48 (m, 1H), 4.85-5.05 (m, 2H), 5.72-5.96 (m, 1H); 13 C
NMR: δ 13.9, 22.8, 23.1, 25.0, 34.6, 35.8, 46.2, 63.3, 76.5, 110.7, 116.9, 135.8, 205.4.
(2R,3R,4R/4S)-1,2-Cyclohexylidenedioxy-4-methyl-5-hexen-3-ol 69a or 69d. To a well
stirred and cooled (-78 o C) solution of the ketone 70b or 70c (0.6 g, 2.68 mmol) in THF
(50 mL) was injected K-selectride (3.0 mL, 1M in THF). The mixture was stirred at -78 o C
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