2β-Alkyl derivatives of gibberellin A1

Abstract

In the reaction of gibberellin A₃(1) with lithium dialkylcuprates, anti-S_N2′-type substitution occurred with the displacement of the lactone function. The resultant 2β-alkyl-1(10)-enedioic acids (4)–(7) were iodolactonised, then reductively de-iodinated to give 2β-methyl, 2β-ethyl, 2β-n-propyl, and 2β-n-butyl gibberellin A₁(16)–(19). The reaction of lithium dimethylcuprate with 3-didehydrogibberellin A₃ was complex but there was no evidence for the occurrence of conjugate addition to the α,β-unsaturated ketone in competition with the anti-S_N2′-type reaction.