Diatereoselectivity in the O-H Insertion Reactions of Rhodium Carbenoids Derived from Phenyldiazoacetates of Chiral Alcohols. Preparation of α-Hydroxy and α-Alkoxy Esters

Article abstract of DOI:10.1021/jo00119a023

A series of phenyldiazoacetates 3 derived from enantiomerically pure alcohols ((-)-borneol, (+)-menthol, (-)-menthol, (-)-8-phenylmenthol, (-)-trans-2-phenylcyclohexanol, (+)-trans-2-phenyl-cyclohexanol, and (-)-10-(dicyclohexylsulfamoyl)-D-isoborneol) were prepared from the corresponding α-keto esters 1 by way of the tosylhydrazones 2.Rhodium(II)-catalyzed decomposition of the diazoacetates 3 in the presence of water or alcohols resulted in carbenoid O-H insertion reactions to give the corresponding 2-hydroxy- or 2-alkoxyphenylacetates in good yield, but with varying degrees of diastereoselectivity.A range of rhodium(II) and other metal catalysts were investigated, with rhodium(II) acetate and rhodium(II) acetamide giving the best results.The stereochemistry of the major diastereomer was proved in most cases by independent synthesis from a mandelic acid derivative of known configuration.Possible mechanisms are discussed.