FORMIC ACID-INDUCED ?-CYCLIZATION OF GLYCINE CATION EQUIVALENTS TO SUBSTITUTED PIPECOLIC ACID DERIVATIVES

Article abstract of DOI:10.1016/S0040-4020(01)86444-9

Formic acid-mediated cyclization reactions of N-(3-alkenyl)-N-(methoxycarbonyl)-acetoxyglycine esters are described.The major reaction products are 4-formyloxypipecolic acid derivatives, formed with low stereoselectivity at C-4.The several subtle features of the cyclization process are satisfactorily explained by a mechanism involving (1) a rapid cationic aza-Cope rearrangement of the incipient iminium ion and (2) participation of the ester moiety through formation of a relatively stable bicyclic dioxycarbenium cation as pivotal intermediate.