Allenes. Part 46. Synthesis of 1,2-dihydro-4H-3,1 -benzoxazines, 4H-3,1-benzoxazines, and 3-cyanoquinolines from allenic and acetylenic nitriles

Abstract

Allenic nitriles or phenylpropynenitrile react in refluxing ethanol with o-aminobenzyl alcohol to give first enaminic nitriles (2) which slowly cyclise to dihydro-4H-3,1-benzoxazines (3). The latter eliminate acetonitrile on heating to give 4H-3,I -benzoxazines (4) whereas the enaminic nitriles under the same conditions give mainly 2-alkyl-3-cyanoquinolines (5). Mechanistic considerations and spectroscopic details are discussed.