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If, in a monoester of a 1 : 3-diol, the hydroxyl and ester groups are held close together by their molecular environment, hydrogen bonding to the alcohol oxygen of the ester occurs. Such hydrogen bonding facilitates hydrolysis of the ester, and in cyclohexane compounds the usual rule whereby equatorial esters are more easily hydrolysed than axial esters can be reversed. The r61e of the neighbouring hydroxyl group in these reactions may be regarded as that of an intramolecular electrophil.WITH the intention of finding suitable conditions for selective hydrolyses of 3-acetoxy-5hydroxy-steroids, aqueous potassium hydrogen carbonate was studied, and conditions were thereby found under which a cis-diaxial hydroxy-ester was largely hydrolysed whereas non-hydroxylated esters were unchanged. The four 3-acetoxy-5-alcohols of the (I1 ; 7O0/0) ( I l l ; 1 3 % ) ( 1 V ; 7 8 % ) ( I ; I 8 O I 0 ) cholestane and coprostane series were therefore treated with potassium hydrogen carbonate solution under identical conditions-the percentage hydrolysis of each is shown below the formulae (1)-(IV). The facilitating effect of a hydroxyl group cis to an ester group part I, preceding paper.

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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.