The Clemmensen reduction of β-diketones

Development of Palladium-Catalyzed Cycloalkenylation and its Application to Natural Product Synthesis

“…GA 12 (37), GA 111 (52), and GA 112 (53) belong to C 20 gibberellins, and GA 12 (37) is believed to be a common intermediate in the biosynthesis of all gibberellins. The latter possesses ent-gibberellane framework.…”

“…The latter possesses ent-gibberellane framework. Since the question of how to establish practical routes for the construction of C 20 gibberellins was open, we made a start in the study of a stereoselective synthesis of C 20 gibberellins, such as GA 12 (37), GA 111 (52), and GA 112 (53), employing the palladi- um-catalyzed cycloalkenylation developed as above ( Figure 2). 29 The CD ring system of gibberellins consists of bicyclo[3.2.1]octane ring system.…”

“…After functional group adjustments of 62, total syntheses of GA 12 (37), GA 111 (52), and GA 112 (53) were achieved as their methyl esters (Scheme 12). Namely, successive conjugate reduction of 62 and stereoselective methylation gave the ester 63, which was converted to the diol 64, by DIBALH reduction, followed by debenzylation under Birch reduction conditions.…”

The mechanism of the biosynthetic oxidation of caranine and derivatives

“…Several theories have been proposed to explain the biosynthesis of the carbon skeleton of these alkaloids (3,4,5,6). The hypothesis of Barton and Cohen (5) that the alkaloids were built up by oxidative coup ling of phenolic intermediates of the norbelladine type, has been experi mentally substantiated by feeding experiments with radioactively labeled materials.…”

“…Several theories had been proposed to explain the biosynthesis the lycorine ring system (3,4,5,6). The theory that has now gained the most acceptance is that proposed by Barton and Cohen in 1957 (5).…”