Synthetic Plant Growth Regulators. IV. The Preparation of Hydroxylated Helminthosporic Acid Analogues

Abstract

Sequential reduction (sodium borohydride, metal-ammonia, hydrogenation) of ketone (8) gave the hydroxy ketone (9) which was converted into olefin (10) (Wittig olefination) and thence to acid (14) by means of the [2,3] sigmatropic rearrangement of ylide (12) to (13). Acid (15) was similarly prepared from alcohol (11) which was obtained by deoxygenation of ketone (9). The tetrahydrocuminic acid (16) was hydroxylated (lithium diisopropylamine, oxygen); the new hydroxyl group was protected with a dichloroacetyl function and then converted into the diazoketone. Lewis-acid-induced cyclization of (17) gave the bicyclooctanone (18a) plus its Δ³-isomer (18b), both of which were reduced and hydrolysed to hydroxy ketone (19). Wittig methylenation of (19) gave olefin (20) which was rearranged by acid to ketone (21). Both (20) and (21) were elaborated further to the acids (6) and (25), respectively, by the procedures used in the preparation of acids (14) and (15).