Substituent Effects in the Ring–Chain Tautomerism of 1‐Alkyl‐3‐arylnaphth[1,2‐e][1,3]oxazines

Abstract

AbstractNew 1‐(1‐aminoalkyl)‐2‐naphthols 8–11 have been synthesised by the condensation of 2‐naphthol with aliphaticaldehydes in the presence of ammonia, followed by acidic hydrolysis. The condensation of 7–11 with substitutedbenzaldehydes after microwave irradiation led to1‐alkyl‐3‐aryl‐2,3‐dihydro‐1H‐naphth[1,2‐e][1,3]oxazines,which proved to be three‐component (rt‐o‐rc) tautomeric mixtures in CDCl3 at 300 K. The electronic effects of the 1‐alkyl and 3‐aryl groups on the tautomeric ratios could be determined for both the ringtrans–chain and the ringcis–chain equilibria with the aid of two‐variant linear equations. A significant difference was found between the coefficients of the Meyer parameter Va, which characterises the volume of the portion of the alkyl substituent within 0.3 nm of the reaction centre, for ringtrans–chain and ringcis–chain equilibria, and this is explained in terms of the stereoelectronic effect caused by the alkyl substituent at position 1. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)