Iodine-mediated one-step synthesis of ipomone from gibberellic acid.

A fast and efficient method for synthesising ipomone ( 4 ), a bicyclo[3.2.1]octanone containing aromatised derivative, from gibberellic acid ( 1 ) has been developed using molecular iodine as a mild and effective mediator under heating conditions in a single step. Evidence was obtained that the reaction simultaneously proceeds through aromatisation and pinacol-pinacolone type 1,2-alkyl shift. Use of excess iodine afforded iodomethyl derivative ( 5 ) that could serve as starting material for the synthesis of additional analogs.