Photo-oxygenation studies of some derivatives of ent-gibberellane

Abstract

Attempts to photo-oxygenate the 2,3- and 16,17-double bonds in some derivatives of ent-gibberellane were unsuccessful except in the case of allogibberic acid (VIII; 9α-H, R = H) and its methyl ester (VIII; 9α-H, R = Me), which reacted at the 16,17-double bond to give the expected 15-en-17-ols (IX; R = H) and (IX; R = Me), respectively. Acid-catalysed rearrangement of the latter (IX; R = Me) gave the hydroxymethyl derivative (X; R = Me) of methyl gibberate, which was identical with the methyl ester of the rearrangement product obtained from gibberellin A₃ 16,17-epoxide (XI; R = H). The major product from the rearrangement of the product of photo-oxygenation of methyl allogibberate was the 7 → 15-lactone (XIII) of 15-hydroxyallogibberic acid.