GIBBERELLINS-LXXXIX. SYNTHESIS OF GIBBERELLIN A55 AND A57 AS WELL AS 1-OXYGENATED GIBBERELLIN A5 AND A20 ANALOGUES-A NEW PRINCIPLE FOR THE REGIOSELECTIVE TRANSPOSITION OF AN ALLYLIC ALCOHOL FUNCTION

Article abstract of DOI:10.1016/S0040-4020(01)88545-8

The synthesis of a series of 1-oxygenated gibberellins starting from GA₃ (1) is described.Nucleophilic addition of hydrazoic acid to 3-dehydro GA₃ (2) was followed by NaBH4 reduction of the resulting 1-azido-3-ketones 4 and 5 to the corresponding azido alcohols 8-10, and photolysis of the latter compounds to instable 1-imines which were smoothly hydrolysed to the 1-oxo-3-hydroxy gibberellins 13 and 14.Subsequent NaBH4 reduction led to GA₅₇ (19) and GA₅₅ (20) and their 3-epimers, 17 and 18 respectively.In further steps 1-oxo-GA₅ (21), 1α- and 1β-hydroxy-GA₅ (23 and 24), 1-oxo-GA₂₀ (25) as well as 1α- and 1β-hydroxy-GA₂₀ (26 and 27) were available.The structures of the synthesized gibberellins were determined by physical data, in regard to the stereochemistry at C-1 and C-3 especially on the basis of 1H NMR and ORD measurements.