DIRECT SYNTHESIS OF 3,4-DIHYDRO-2H-PYRIDO[1,2-A] PYRIMIDINES, BY ADDITION-REACTIONS WITH 2-AMINOPYRIDINES

Reaction of 2-aminopyridines with formaldehyde and electron rich alken es permits synthesis of pyridopyrimidines by formation of imines and s ubsequent addition to the alkenes in a formal aza Diels Alder reaction . The structure of the cyclic amidine products is confirmed by single crystal X-ray analysis on a neutral amidine isolated from an aminopyri dine substituted with an electron withdrawing trifluoromethyl group an d of a trifluoroacetate salt of an amidine obtained from 2-aminopyridi ne, formaldehyde and indene. These structural studies permit the regio - and stereo-chemical outcome of these addition to be defined mid comp ared with related processes. Copyright (C) 1996 Published by Elsevier Science Ltd