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.