2β-Isopropylidene-, 2β-t-butyl-, and 2β-isopropyl-gibberellin A4 and spiro[gibberellin A4-2,1′-cyclopropane]
Abstract
2-Bis(methylthio)methylene-3-oxogibberellin A9methyl ester (9), prepared from 3-oxogibberellin A9methyl ester (25), was used as a synthon to prepare 2-isopropylidenegibberellin A4(14), 2β-t-butylgibberellin A4(18), 2β-isopropylgibberellin A4(22), and spiro[gibberellin A4-2,1′-cyclopropane](48). Spiranation of 3-oxogibberellin A9methyl ester (25) was also achieved directly by reaction with 2-chloroethyldimethylsulphoxonium iodide. The preparation of 2α-alkyl derivatives of gibberellin A4from the synthon (9) was not achieved, hydride reduction of the 2α-alkyl 3-ketones giving the 3α-hydroxy epimers.