AN UNEQUIVOCAL SYNTHESIS OF 5,6,8-TETRAHYDROPYRIDO[2,3-D]PYRIMIDINE-2,7-DIONES AND 5,6,8-TETRAHYDROPYRIDO[2,3-D]PYRIMIDINE-4,7-DIONES

An unequivocal set of procedures for the synthesis of 5,6,8-tetrahydro pyrido[2,3-d]pyrimidine-2,7-diones (7) and 2-amino-3,5,6,8-tetrahydrop yrido[2,3-d]p (8), in a maximum of four seeps from an alpha,beta-unsat urated ester 1, is reported. Thus, the acid hydrolysis of the 2,4-diam inopyrido[2,3-d]pyrimidines 3 yields the 4-amino-2-oxopyrido[2,3-d]pyr imidines 7 while the cyclization of the Michael adducts 9 (formed by r eaction of 1 and methyl cyanoacetate) with guanidine affords the corre sponding 2-amino-4-oxopyrido[2,3-d]pyrimidines 8. Both isomers were al so obtained by hydrolysis of the 4-amino-2-bromo- and bromo-5,6-dihydr opyrido[2,3-d]pyrimidin-7(8H)-ones 5 and 6, respectively.