Sequential addition reaction of lithium acetylides and Grignard reagents to thioiminium salts from thiolactams leading to 2,2-disubstituted cyclic amines

The reaction of thioiminium salts derived from gamma- and delta-thiolactams with lithium acetylides and Grignard reagents proceeded sequentially to give 2,2-disubstituted pyrrolidines and piperidines in moderate to high yields. In the initial step of the reaction, 2-(methylthio)pyrrolidines and -piperidines may be formed. The use of lithium (trimethylsilyl)acetylide gave the products most effectively. Aryl-, alkyl-, and allylmagnesium halides were used as Grignard reagents. Silylcarbocyclization of N-allyl 2-ethynyl cyclic amines with HSiMe2Ph in the presence of a catalytic amount of Rh-4(CO)(12) was carried out to give trisubstituted hexahydro-1H-pyrrolizines and octahydroindolizines. (c) 2006 Elsevier Ltd. All rights reserved.