The Dimroth rearrangement. Part XVIII. Syntheses and rearrangement of 4-iminoquinazolines and related systems

Abstract

o-Aminobenzonitrile is converted by triethyl orthoformate–acetic anhydride into its N-ethoxymethylene derivative (2), which can undergo alkylaminolysis followed by spontaneous cyclization to 3-alkyl-3,4-dihydro-4-iminoquinazolines (3; X = CH); these rearrange in alkali to 4-alkylaminoquinazolines. The related 3,4-dihydro-4-imino-2,3-polymethylenequinazolines (8; X = NH) are also prepared from o-aminobenzonitrile, either by condensation with appropriate cyclic imino-ethers or by cyclodehydration with lactams; when the 2,3-polymethylene chain is longer than five CH₂ units, Dimroth rearrangement occurs in alkali to give the isomeric β-bridged 2,N(4)-polymethylene-4-aminoquinazolines (9; X = CH). Aza-analogues of the above systems are prepared by analogous routes. Rates of rearrangement are discussed.