Synthese von 5-Methyl-3-oxa-A-nor-5β-cholestan und 3-Oxa-Δ4-cholesten-2-on

2, 3-seco-Δ⁴-Cholestene-2, 3-dicarboxylic acid ( 5 ) was prepared in 30% yield from 2-hydroxymethylene-Δ⁴-cholestene-3-one ( 1 ) by ozonolysis under special conditions. Pyrolysis of the pure di-acid 5 gave A-nor-Δ³⁽⁵⁾-cholestene-2-one ( 6 ), the anhydride 2 and 5-methyl-3-oxa-A-nor-5β-cholestane-2-one ( 8 ). Pyrolysis of amorphous acidic material obtained by the ozonolysis of 1 yielded the enol-lactones 7 and 9 as additional products. LiA1H₄-reduction of the γ-lactone 8 gave the diol 10 , which was transformed into 5-methyl-3-oxa-A-nor-5β-cholestane ( 13 ) by treatment with tosyl chloride in pyridine.