Anomalous Reaction Course in the Amidoalkylation With 4‐Substituted 2‐Methoxy N‐Trifluoroacetyl Piperidines

Amidoalkylation of suitably substituted benzo[b] furans and benzo[b] thiophenes with 2-methoxy-N-acyl-piperidines and morpholines gave very low yields of the 2-(2'-benzo[b] furanyl)-, and 2-(2'-benzo[b] thienyl) piperidine derivatives. The amidoalkylation of 3-phenyl-benzo[b] furan with the isomeric mixture of the 4-methyl-2-methoxy-N-trifluoroacetyl piperidines however gave a good conversion but trans-4-methyl-2-(2'-(3'-phenyl) benzo[b] furanyl)-N-trifluoroacetyl piperidine is only the minor product formed. Mass spectroscopy, H and 13C NMR spectroscopy proved that the major product is l-trifluoroacetylamino-3-methyl-5, 5-bis (2'-(3'-phenyl)-benzo[b] furanyl)-pentane.