Enamines, cyclic

Ketene acetals show a pattern of product formation very similiar to enamines79 Diphenyl-4,4-diacetyl triafulvene is converted to diacetylmethyl cyclopentadiene 529 by S,N-acetals, whilst diphenyl-4,4-dicyano triafulvene undergoes C—C-inser-tion to S,N- and N,N-acetals, e.g. 530/531, resulting in cross-conjugated systems 533/534 by analogy with enamines. Cyclic S,N-acetals 532, however, yield exclusively the bicyclic fulvenes 535 due to additional loss of methyl mercaptan. 

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