Formation of polysubstituted 1,2,5,6-tetrahydropyridines from the 4+2 cycloaddition reaction of bis(phenylsulfonyl)butadienes with aryl imines
摘要:
The reaction of 2,3-bis(phenylsulfonyl)-1,3-butadiene with aryl imines affords N-alkyl-3,5-bis(phenylsulfonyl)-1,2,5,6-tetrahydropyridines in high yield. The formation of the rearranged cycloadducts proceeds by a mechanism that involves addition of benzenesulfinate anion onto the terminal pi-bond of the activated diene. The resulting carbanion undergoes proton transfer followed by aryl sulfinate ejection to give 1,3-bis(phenylsulfonyl)-1,3-butadiene as a transient intermediate. This reactive diene undergoes a rapid 4 + 2 cycloaddition followed by a subsequent hydrogen 1,3-shift. Support for the proposed mechanism is provided by the observation that a mixed cycloadduct is obtained from the reaction of a 1:1 mixture of 2,3-bis(phenylsulfonyl)- and 2,3-bis[(o-nitrophenyl)sulfonyl]butadiene with N-benzylidenemethylamine. An additional piece of supporting data for the proposed mechanism is the much shorter reaction time necessary for the reaction to go to completion when a small amount of sodium benzenesulfinate is added to the reaction mixture. 1,3-Bis(phenylsulfonyl)butadiene was independently synthesized by two different routes. This diene was found to rapidly react with a variety of imines to give the same cycloadducts as those derived from the 2,3-isomer. The reaction of several 4-substituted 1,3-bis(phenylsulfonyl)butadienes with aryl imines was found to give related 4 + 2 cycloadducts.
benzonitriles is achieved via amino-catalyzed [3+3] benzannulation of α,β-unsaturated aldehydes and 4-arylsulfonyl-2-butenenitriles. Using pyrrolidine as an organocatalyst via iminium activation, a series of substituted benzonitriles were obtained in good to high yields in a regioselective manner. This reaction can proceed smoothly under mild reaction conditions and without the aid of any metals, additional