TOWARDS THE SYNTHESIS OF THE C-37-C-42 FRAGMENT OF RAPAMYCIN - INTRAMOLECULAR REACTIONS OF ALLYL SILANES WITH OXONIUM IONS GENERATED FROM ALPHA-ALKOXY SULFONES

A new method for the formation of methylene cyclohexane derivatives has been developed, using intramolecular trapping by allyl silanes of oxonium ions generated from alpha-alkoxysulfones. These acyclic precursors were prepared by quenching the anion of methoxymethyl phenyl sulfone 2 with various electrophiles containing the ally] silane moiety. When a beta-substituent is present, the stereochemical outcome of the cyclisation reaction has proved to be dependant on the stereochemistry of the starting material. This methodology has been applied to the synthesis of 1, a synthetic precursor to the C-37-C-42 fragment of rapamycin.