Bufadienolides. 32. Selenium Dioxide Dehydrogenation of 14-Dehydrobufalin

Article abstract of DOI:10.1021/jo00347a026

Unlike digitoxigenin acetate (1), bufalin acetate (5a), resibufogenin acetate (6a), and cinobufagin acetate (6b) were found to be resistant to selenium dioxide hydroxylation (e.g., 1 -> 2).However, under similar conditions selenium dioxide was found to dehydrogenate 14-dehydrobufalin (7a) to 3β-hydroxy-5β-bufa-8,14,20,22-tetraenolide (8a).An analogous dehydrogenation reaction was observed by employing 14-dehydrobufalin acetate (7b -> 8b).The structure of tetraene 8 was confirmed by dehydration of alcohol 10 to yield the same tetraene (8b).In turn, the structure of alcohol 10 prepared from α-epoxide 9 was substantiated by an X-ray crystallographic study of o-nitrobenzoate derivative 11.