Heteroannulation of 2‐amino‐6‐thioxouracil: A new access for the synthesis of fused pyrimidine derivatives

In current work, heteroannulation of 2‐amino‐6‐thioxouracil to new fused pyrimidine scaffolds is described, where pyrimidine 1 undergoes cyclocondensation with pyruvic acid derivative 2 and ninhydrin ( 6 ) to furnish thiopyranopyrimidine 5 and thienopyrimidine 8 , respectively. Alkylation of aminopyrimidine 1 with benzyl chloride consumed two moles to form S ‐ and N ‐alkylated product 9 . Subjecting compound 9 to aminolysis with aniline derivatives resulted in 4‐aminopyrimidine 10a , b through Dimorth rearrangement. Furthermore, the addition of cyclic enamine 10a , b to ninhydrin and benzoyl isothiocyanate produced pyrimidine derivatives 12a,b and 14 . Finally, the addition of enamenic carbon of 10a , b to polarized systems 2 or 18 afforded the pyrido[2,3‐ d ]pyrimidines 17 and 21a‐d in moderate to good yield.