Lanosterol has been converted into 3~-acetoxylanost-7-en-32-onitrile and thence into 3p-acetoxylanost-7-en-32al and 3p.32-diacetoxyIanost-7-ene. 3 p-Acetoxy-I 1 -0xolanost-8-en-32-onitrile and methyl 3p-acetoxy-32nitrilo-I 1 -oxo-25,26,27-trinorlanost-8-en-24-oate have been synthesised by an analogous route. Unsuccessful attempts to prepare 3p-acetoxylanost-7-en-32-oic acid are reported, together with some novel methods for the oxidation of sterically hindered aldehydes as exemplified by using pivalaldehyde as a model compound.CONSIDERABLE importance has been ascribed to 32oxygenated derivatives of lanosterol as probable intermediates in the biosynthesis of cholestero1.l We report the synthesis of such compounds via the photolysis of the nitrite esters of a number of 7a-hydroxylanostane derivatives; preliminary accounts of part of this work have appeared.2 Similar studies have been undertaken by two other groups of ~o r k e r s .~J Further to their synthetic work, Fried and his co-workers demonstrated the efficient conversion of both lanost-7-ene-3p,32-diol and 3p-hydroxylanost-7-en-32-al into cholesterol by rat liver h~mogenates.~ 3~-Acetoxylanostan-7a-ol (11; R = H, X = Me) was prepared by catalytic hydrogenation of 3p-acetoxylanostan-7-one (I) .6 Treatment of the product with nitrosyl chloride in anhydrous pyridine gave the crystaline 7a-nitrite (11; R = NO, X = Me). Photolysis of the latter in benzene using a high-pressure mercury arc lamp with a Pyrex filter afforded the oxime (11; R = H, X = CH:N*OH) in 60% yield, together with minor amounts of the alcohol (11; R = H, X = Me) and the ketone (I) .8 Confirmation of the structure assigned to the oxime was obtained by its conversion into 3p,7adiacetoxylanostan-32-onitrile (11; R = Ac, X = CN) using fused sodium acetate in refluxing acetic anhydride. Acetylation of the oxime under milder conditions (acetic anhydride-pyridine at room temperature for 1 h) gave the intermediate product, 3~-acetoxy-32-acetoxyiminolanostan-7a-01 (11; R = H, X = CH:N*OAc), which at its m.p. eliminated acetic acid to give 3p-acetoxy-7ahydroxylanostan-32-onitrile (11; R = H, X = CN). This latter compound was more conveniently prepared by heating the acetoxy-imine (11; R = H, X = CHIN-OAc) in pyridine at 90" for 1 h.Reduction of 3 ~-acetoxy-32-hydroxyiminolanostan-7a-01 (I1 ; R = H, X = CH:N*OH) with zinc in glacial acetic acid afforded 3p-acetoxy-7a,32-epoxylanostane (I11 ; R1 = R2 = H), identical with a sample prepared by the thermal reaction of 3 p-acetoxylanost an-7 a-01 with lead t etra-acet ate .3b A correlation between 32-f unctionalised 1 ( a )
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