Synthesis of substituted 9-Oxo-9,10-dihydroacridine-4-carboxylic acids. I. Factors affecting the direction of ring closure of substituted N-(2-Carboxyphenyl-amino)benzoic acids

Abstract

The cyclodehydration of 16 substituted N-(2-carboxyphenylamino)benzoic acids to substituted 9-oxo-9,10-dihydroacridine-4-carboxylic acids with conc. H₂SO₄, POCl₃ and ethyl polyphosphate (epp) has been studied by h.p.l.c. Direction of ring closure can be qualitatively interpreted in terms of the electronic and steric effects of the substituent group on the carbonium ion intermediate formed from the carboxylic acid group on the same ring as the substituent. Judicious choice of substituents and cyclizing reagents can provide a large excess of one isomer; hence this is a simple route to certain substituted 9-oxo-9,10-dihydroacridine-4-carboxylic acids.