Synthetic plant growth regulators. I. The synthesis of (±)-14-Norhelminthosporic acid and related compounds

Cuminic acid (9) was converted by reductive methylation into 1,2,3,6-tetrahydro-4-isopropyl-1- methylbenzoic acid (12). Acid-catalysed cyclization of the diazomethyl ketone (8) derived from (12), followed by hydrogenation, gave the bicyclo[3,2,l]octanone derivative (7), which was then converted through the allylic bromide mixture of (18) and (19) into the p-toluenesulphonyldithiocarbazone (21) and the allylic ammonium bromide (25). The [2,3]-sigmatropic rearrangement of the dithio- carbene derived from (21) and the ylid derived from (25) afforded the dithioester (22) and pyrrolidine (26), respectively, from which the alcohol (24), aldehydes (27) and (28), and acids (5) and (6) were prepared. Bioassay of (5), (6), (27) and (28) indicated gibberellin-like properties for all these compounds with potency comparable with that of helminthosporic acid (2).