Unusual reactions of methylsulfonyl esters: Syntheses of 3 alpha-methyl and 3 beta-methyl gibberellin A(20)

Gibberellin A(3) has been converted to 3 alpha-methylGA(20) 8 in 33% yield via catalytic hydrogenation of the 3-exo-methylene derivative 14. In an attempt to prepare 3 beta-methylGA(20) 9, the 3 alpha-methanesulfonate 25 has been treated with lithium dimethylcuprate; only the beta-keto sultones 26 and 27 have been isolated (84% yield). In contrast, under similar conditions the 3 alpha-methanesulfonate 35 gave the 2-oxopropylsulfonyloxy derivatives 36 and 37. Synthesis of 3 beta-methylGA(20) has been achieved via reaction of the 3 alpha-trifluoromethanesulfonate 38 with lithium dimethylcuprate. 3 alpha-MethylGA(20) and 3 beta-methylGA(20) show similar activity to GA(20) (and significantly less activity than GA(3)) in the stimulation of stem elongation of dwarf rice seedlings.