摘要:
A new pathway to 1-alpha,2-alpha-methylenegibberellines via pyrazoline intermediates is reported. In contrast to the addition of diazomethane to the DELTA-1-double bond of corresponding enones in the case of 1 "Umpolung" of the regioselectivity with cis-addition from the a-side to give pyrazoline ester 4 is observed. Subsequent photolysis of 4 leads to the 1,2-cyclopropyl derivative 6. The structures of the key compounds 4 and 6 are confirmed especially by n.m.r. and X-Ray analysis.