Methodology for the synthesis of 11,13-dihydroxy gibberellins

A general procedure has been established for the synthesis of 11,13-dihydroxy gibberellins. The key steps involve the isomerization of the 19,10 lactone functionality to the 19,2-isomer, bromination at C-1 and C-11, then selective nucleophilic displacement of the 11-bromo substituent by acetate with silver(1) acetate. Reconstitution of the 19,10 lactone functionality was effected by bromolactonization of a Δ9-ene 19-carboxylic acid to give a 9β-bromo 19,10-lactone followed by stereoselective hydrogenolysis of the bromo substituent