2928 J. Org. Chem., Vol. 39, No. 19, 1974 Notes lution (24 hr at 77O, no isomerization observed after 24 hr at 20'1, a rapid process. Its instantaneous concentration, hence, will be higher than that of 4a, permitting preparative separation. The ease of isomerization of 4a to 5a most likely results from relief of steric strain on ring opening in the 12-diphenyl derivative; no such (kinetic and thermodynamic) driving force exists for the conversion of 4b to 5b. A ...
