Reduction of 5-(bromomethyl)-1-pyrrolinium bromides to 2-(bromomethyl)pyrrolidines and their transformation into piperidin-3-ones through an unprecedented ring expansion-oxidation protocol
摘要:
3,3-Dialkyl-5-(bromomethyl)-1-pyrrolinium bromides, prepared via bromocyclization of N-(2,2-dialkyl-4-pentenylidene)amines by means of bromine in dichloromethane, were reduced to 4,4-dialkyl-2-(bromomethyl)pyrrolidines for the first time using borane dimethyl sulfide in dichloromethane. Furthermore, the latter 2-(bromomethyl)pyrrolidines were transformed into the corresponding piperidin-3-ones through an unprecedented ring expansion-oxidation protocol in dimethylsulfoxide in the presence potassium carbonate. Reduction of 5,5-dialkylpiperidin-3-ones by means of sodium borohydride in methanol afforded 5,5-dialkyl-3-hydroxypiperidines in good yields. (C) 2008 Elsevier Ltd. All rights reserved.
Rearrangement of 5-(bromomethyl)-1-pyrrolinium salts into functionalized piperidines
摘要:
5-(Bromomethyl)-1-pyrrolinium bromides undergo rearrangement with alkoxides in the corresponding alcohol to afford 2,5-dialkoxypiperidines, which are easily converted into 3-alkoxypiperidines. 2,5-Dialkoxypiperidines undergo a peculiar thermal rearrangement to afford 5-alkoxy-1,2,3,4-tetrahydropyridines. Copyright (C) 1996 Elsevier Science Ltd