CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

1H), 3.72-4.00 (m, 4H), 5.22-5.53 (m, 2H), 7.22-7.54 (m, 10H). Anal. Calcd. for
C 20 H 26 O 2 Si: C, 73.59; H, 8.02%. Found, C, 73.65; H, 8.08%.
1-Bromo-4-(tert)-butyldiphenylsilyloxy-2Z-butene 82. To a cooled (0 o C) and stirred
solution of compound 81 (10.0 g, 30.67 mmol) in Et 3 N (20 mL) was added MsCl (4.21 g,
36.80 mmol) and the solution was stirred for 3 h (cf. TLC). Water and EtOAc was added to
the mixture, the organic layer separated and the aqueous layer extracted with EtOAc. The
combined organic extracts were washed with water and brine, and dried. Removal of
solvent in vacuo afforded the crude product.
A mixture of the above crude product and NaBr (4.0 g, 44.55 mmol) in acetone (50
mL) was stirred for 4 h. The reaction mixture was diluted with water, the organic layer
separated and the aqueous layer extracted with EtOAc. The combined organic extracts
were washed with water and brine, and dried. Removal of solvent in vacuo followed by
chromatography (silica gel, 5-10% EtOAc/hexane) afforded pure 82. Yield: 10.73 g (90%);
Light yellow oil; IR: 3063, 3030 cm -1 ; 1 H NMR: δ 1.04 (s, 9H), 3.80-3.92 (m, 2H), 4.11-
4.32 (m, 2H), 5.32-5.50 (m, 2H), 7.21-7.53 (m, 10H). Anal. Calcd. for C 20 H 25 BrOSi: C,
61.69; H, 6.47%. Found, C, 61.73; H, 6.52%.
1,2-Cyclohexylidenedioxy-4-C-(tert)-butyldiphenylsilyloxy-5-hexene-3-ol 83a-d. As
described before, the reaction between 1 (3.50 g, 20.56 mmol) and 82 (8.0 g, 20.56 mmol)
was carried out using bi-metal system or Zn dust. For the Zn-mediated reaction, aqueous
saturated NH 4 Cl was used for the activation of Zn. After the work up, the crude product, in
each case was subjected to column chromatography (silica gel, 0-20% EtOAc/hexane) to
isolate the mixture of 83a and 83b, pure 83c and 83d. The R f (20% EtOAc/hexane) values
of 83a/83b, 83c and 83d were 0.60, 0.57, 0.51 and 0.45 respectively.
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