Oxazoline chemistry part III. Synthesis and characterisation of [2‐(2′‐anilinyl)‐2‐oxazolines] and some related compounds

Abstract

Abstract The syntheses and characterisation of a series of chiral and achiral 2‐(aminophenyl)‐2‐oxazolines and some related compounds is reported. All of the derivatives have been produced by a one‐step procedure involving the treatment of isatoic anhydride ( i.e. [2 H ]‐3, 1‐benzoxazine‐[1 H ‐2,4‐dione: 1 ) or its 5‐chloro analogue with a slight excess of appropriate amino‐alcohols. In most cases, anhydrous ZnCl 2 is shown to be an effective Lewis acid catalyst for this reaction at reflux temperature in high boiling aromatic solvents (PhCl or PhMe). Oxazolines have been readily formed using rac ‐2‐amino‐1‐butanol, ( S )‐phenylglycinol, 2‐methyl‐2‐amino‐1‐propanol and (1S,2R) or (IR,2S)‐cis ‐ 1 ‐amino‐2‐indanol; yields range from 85% to 22%. The use of aminoalcohols such as 2‐ethanolamine, (±)‐2‐amino‐1‐phenyl‐1‐propanol or 3‐amino‐1‐propanol (to give the corresponding 4,5‐dihydro‐1,3‐oxazine) results in poor yields. The use of other Lewis acid catalysts (silicic acid, Cd(acac) 2 ·2H 2 O, CuCl 2 ·2H 2 O, InCl 3 ) or higher temperatures did not improve the yields with these latter two substrates. Benzoxazoles and N‐substituted benzoxazoles can also be obtained in reasonable yields from 1 using 2‐aminophenol (36%) or 2‐amino‐3‐hydroxypyridine (45%).