Synthesis of 2,4‐Diaryl‐3,4‐dihydro‐2H‐naphth[2,1‐e][1,3]oxazines and Study of the Effects of the Substituents on Their Ring‐Chain Tautomerism

A number of 2‐(α‐amino‐Y‐substituted‐benzyl)‐1‐naphthol hydrochlorides were prepared by a convenient Mannich‐type aminoalkylation. 2,4‐Diaryl‐3,4‐dihydro‐2H‐naphth[2,1‐e][1,3]oxazines were prepared through the ring‐closure reactions of the starting aminonaphthols with aromatic aldehydes, which proved to furnish three‐component (ring1−open−ring2) tautomeric mixtures in CDCl3 at 300 K. The electronic effects of the 2‐aryl groups on the ratios of the ring‐chain tautomeric forms at equilibrium could be described by Equation (1). Study of the effects of substituents X and Y on the tautomeric equilibria [by the aid of the multiple linear regression analysis of Equations (2) and (3)] revealed that the trans‐chain equilibrium constants are significantly influenced by the inductive effect (σF) of substituent Y on the 4‐phenyl ring. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)