Heterocyclization of N-propenyl-substituted phenothiazines and phenoxazines using electrophiles in an anhydrous medium

Abstract

The high interest in the chemistry of phenothiazine and phenoxazine is due in many ways to the biological activity of their derivatives [1][2][3][4][5]. We have previously reported the prototropic isomerization of N-allyl derivatives of phenothiazine and phenoxazine to give cis-10-propenylphenothiazine (1) [6] and cis-10-propenylphenoxazine (2) [7]. In the case of the acid hydrolysis of these compounds it has been shown [8] that they demonstrate an increased activity with relation to electrophilic reagents while the initial position of attack of a proton to form the carbenium-immonium intermediate of type A is the α-carbon atom of the substituent (Scheme 1). Scheme 1 N X N X BF 3 ·Et 2 O + 1, 2 A1, A2 1, A1 X = S, 2, A2 X = O _______ * Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his jubilee. __________________________________________________________________________________________