Terf-butyldiphenylsilyl ether

S, Hanessian and P. LavalKe, The preparation and synthetic utility of terf-butyldiphenylsilyl ethers, Can. J. Chem. 53 2975 (1975). 

Model studies aimed at the synthesis of Calyculin discovered a subtle effect of a remote protecting group on the stereoselectivity of an epoxidation reaction [Scheme 1,46], 79 Treatment of the unprotected diol derivative 46.1 with potassium carbonate, benzonitrile and hydrogen peroxide gave a diastereoisomeric mixture of epoxides 46.2a,b (3 1) in favour of 46.2a. However, the same reaction performed on the terf-butyldiphenylsilyl ether 463 both increased the selectivity (1 18) and inverted its sense now 46 4b was the major product. 

Scheme 4 depicts the remainder of our total synthesis. The acid (5) was subjected to RedAl reduction to give the hydroxymethyl intermediate (6) in 99 % yield, which was then protected as the terf-butyldiphenylsilyl ether (7) under standard conditions (96 %). Silicon-mediated fragmentation of the acetonide (7) was carried out under Lewis acid-mediated conditions (BF, OEtj) to fiimish allylic alcohol (8) in 96 % yield. Sharpless epoxidation provided (9), followed by a diastereosclective diimide reduction of the remaining oleHn, to give the epoxyalcohol (10) in satisfactory yield, uid as exclusively one diastereoisomer. 

The dependence of the acid-lability of trialkylsilyl and related ethers on the type of substitution at silicon is illustrated by the formation302 of l-0-(tert-butyldiphenylsilyl)-2,3 4,5-di-0-methylene-D-mannitol (47) in 96% yield on treatment of 6-0-(terf-butyldimethylsilyl)-l-0-(fert-butyldiphenylsilyl)-2,3 4,5-di-O-methylene-D-manni-tol (48) with 80% acetic acid. 

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