953. Studies in the steroid group. Part LVI. Reduction of dehydroergosterol epidioxide

Abstract

A study of the hydrogenation of dehydroergosterol epidioxide and its esters (I) in the presence of platinum catalysts has shown that the ethylenic bond in ring B is reduced first, this being followed by fission of the epidioxide bridge to yield 5 : 8-dihydro~y-A~(1~)-steroids (e.g., 111) ; under carefully chosen conditions either of these stages of reduction can be achieved without hydrogenation of the side-chain double bond. Hydrogenation of (I) in the presence of Raney nickel (or palladium) leads to the formation of 5-hydroxy-A' ' g'll)-steroids, the 22 : 23-bond being unaffected.

Acetyl Chloride

“…171 Examples of selective acetylations involving AcCl include: acetylation of primary alcohols in the presence of secondary alcohols by AcCl/2,4,6-collidine or i-PrNEt 2 (CH 2 Cl 2 , −78 • C); 8,172 acetylation of primary alcohols in the presence of secondary alcohols, 173 and secondary alcohols in the presence of tertiary alcohols, 174 by AcCl/pyridine (CH 2 Cl 2 , −78 • C); monoacetylation of a 2,4-dihydroxyglucopyranose by AcCl/ pyridine/−15 • C (Ac 2 O/pyridine/0 • C is less selective); 175 and acetylation of steroidal 5α-hydroxyls (not 5β) by AcCl/PhNMe 2 (CHCl 3 , ). 176 Although Ac 2 O/DMAP 177 and Ac 2 O/Bu 3 P 170 are the preferred reagents for acetylation of most hindered alcohols, satisfactory results can be obtained with AcCl in combination with PhNMe 2 (CHCl 3 , ), 178 PhNEt 2 (CHCl 3 , ), 179 AgCN (benzene or HMPA, 80 • C), 180 magnesium powder (Et 2 O, ; 45-55% yield of t-BuOAc), 181 and Na 2 CO 3 (cat. PhCH 2 NEt 3 Cl, CH 2 Cl 2 , ; 79% yield of t-BuOAc).…”