Rhodium carbenoid O-H insertion reactions with phenols; A facile method for the synthesis of trialkyl 2-aryloxyphosphonoacetates and their use in the preparation of 2-aryloxy-3-phenylpropanoates.

Abstract

A variety of substituted phenols undergo a facile and hitherto unreported rhodium carbenoid mediated O-H insertion reaction with trialkyl 2-diazophosphonoacetates 7 to afford the corresponding trialkyl 2-aryloxyphosphonoacetates 5 in generally good to excellent yield. Phenols containing strongly electron withdrawing groups, bulky ortho-substituents or certain ortho-heteroatom substituents show reduced or variable yields. Catechol affords a mono-adduct which cyclises to lactone 9. Aniline inserts preferentially and exclusively over phenol in a competition reaction with 7 to afford an anilinophosphonoacetate 11. Phenol insertion products 5 are shown to be versatile intermediates in a novel preparation of 2-aryloxy-3-phenylpropenoates 12 by Wadsworth-Emmons reaction with benzaldehydes. Dissolving magnesium metal reduction provides a mild method for the conversion of the propenoates 12 into the corresponding propanoates 13.