Ta. Spencer et al., Further studies on the synthesis of 24(S),25-epoxycholesterol. A new, efficient preparation of desmosterol, J ORG CHEM, 65(7), 2000, pp. 1919-1923
Efforts to improve the synthesis of 24(S),25-epoxycholesterol (1) from stig
masterol (3) have included identification of 6 alpha-hydroxy-i-steroid 11 a
s a byproduct from the ozonolysis of 9 and an attempt to effect conversion
of sulfone 14 to diol 18 via Payne rearrangement and nucleophilic trapping
of epoxide 25, which led instead to 27 and 28 (97% yield). A more efficient
synthesis of 1 was achieved via coupling of cuprate 21 with allylic acetat
e 31 to give 73% of 16, in the most efficient conversion yet of a C22 inter
mediate to desmosterol (5) or its acetate 6.