Formic acid-induced π-cyclization of glycine cation equivalents to substituted pipecolic acid derivatives

Add time:08/05/2019    Source:sciencedirect.com

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.

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