ACID-CATALYZED CYCLIZATION OF 1,19-UNSUBSTITUTED A,C-BILADIENES

A new route for the synthesis of corroles through cyclization of a,c-b iladienes in acidic media is reported. Spectroscopic analysis of the r eaction mixture shows that it proceeds with an intramolecular pathway through the formation of a totally conjugated open-chain tetrapyrrole, The presence of substituents at the 10-position of the tetrapyrrole s trongly influences the fate of the reaction: phenyl groups accelerate the cyclization to corrole, whereas in the presence of alkyl substitue nts this reaction does not occur. This effect has been examined by mea ns of computational methods, and it has been demonstrated that conform ational factors are dominant in driving the reaction toward the format ion of the macrocycle.