Basic intramolecular acylation. Synthesis of 2-aryl-1-tetralones bearing isopropoxy or benzyloxy groups, synthetic key intermediates for phenolic antileukaemic benzo[c]phenanthridine alkaloids, from 2,4-diarylbutyric acid derivatives

Abstract

Generally applicable intramolecular cyclisation of 2,4-diarylbutyric acids having isopropoxy (4) or benzyloxy (12) groups used to protect phenolic functions was required for the purpose of synthesis of phenolic benzo[c]phenanthridine alkaloids. Treatment of the butyric acids (4b), (4d), (4f), and (12) with POCl₃ in acetonitrile in the presence of potassium carbonate furnished the corresponding tetralones (5b), (5d), (5f), and (13) in excellent yield, respectively, without the cleavage of its isopropoxy or benzyloxy groups. A plausible mechanism for basic intramolecular acylation using POCl₃, is proposed.