Preparation of 1,3,5(10),9(11)-estratetraenes from 1,3,5(10),8-estratetraenes
Liu L., Li Z., Su X.
The title products are prepd. in high yields via refluxing in protic or aprotic solvents in the presence of arom. sulfonic acids or strong inorg. acids. D-13β-Ethyl-3-methoxy-1,3,5(10),8-gonatetraen-17β-ol in THF contg. NaH was refluxed for 1 h, benzyl bromide was added, and the reaction mixt. was allowed to react for 5 h to give 95% D-117β-(benzyloxy)-3β-ethyl-3-methoxy-1,3,5(10),8-gonatetraene, which was refluxed with 4-MeC6H4SO3H in HOAc-benzene for 9 h to give, after treatment with 10% NaOH, 89% D-117β-(benzyloxy)-3β-ethyl-3-methoxy-1,3,5(10),9(11)-gonatetraene. [on SciFinder(R)]