Abstract
Solvolysis of 3-keto-23-tosyloxy (A) and 3-keto-24-tosyloxy (B) derivatives of triterpenoid with t-butoxide proceeded in stereospecific manner to yield rearranged bicyclo [3, 2, 0] heptanones (C) and (D), being antipodal to one another with respect to the ketonic chromophor, whose structures were respectively established by spectral and chemical means. Reinvestigation of solvolysis for the simplest keto-tosylate (13) confirmed the formation of two bicyclo [3, 1, 1]- (14) and bicyclo [3, 2, 0]-(15) heptanones. The former rearranged by acid to a new bicyclo [3, 2, 0] heptanone (20), while the latter was stable to acid. Based on these evidences a plausible mechanism (Chart 4) of the homo-Favorskii rearrangement (13→15) was proposed. A new method of selectively converting a cyclobutanone to a γ-lactone in high yield was described.
