The enamines having an α-hydrogen, R1R2N-αCH=βCR3CH3, reacted with a variety of benzylideneanilines to provide the [4+2] cycloadducts, 1,2,3,4-tetrahydroquinoline derivatives, in acetic acid or in methanol containing a catalytic amount of p-toluenesulfonic acid in considerable yield.
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Nomura et al. (1978) studied this question.
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