Studies On The Synthesis Of Pyrido[2, 3-d]Pyrimidines

α-Oxo ketene dithioacetals are a kind of versatile intermediates in organicsynthesis. It can be widely used in forming aromatic and heterocyclic compounds.Pyridopyrimidines are heterocyclic compounds along with bio-and pharmacologicactivities. The scientific and practical demands for such compounds are increasing.Therefore, the combination of a-oxo ketene dithioacetals and the synthesis ofpyridopyrimidines deserve investigation.In this thesis, a convenient and efficient synthesis of highly functionalizeddihydropyrido[2,3-d]pyrimidines via a double [5 + 1] annulation strategy startingfrom easily available α-alkenoyl-α-carbamoyl ketene-(S,S)-acetals 1 and cheapreagents (NH4OAc, DMF, and POCl3) has been developed. In the first step of thedouble annulation route, 2-amino-3-carbamoyl-5,6-dihydro-4-pyridones 2 werecreated in high to excellent yields by a formal [5C + 1N] annulation reaction ofketene-(S,S)-acetals 1 with ammonia (from ammonium acetate). In the second step ofthe double annulation strategy, the highly functionalized dihydropyrido[2,3-d]pyrimidine derivatives, 7,8-dihydropyrido[2,3-d]pyrimidin-4(3H)-ones 3 (when R1 =aryl) and 7,8-dihydropyrido[2,3-d]pyrimidines 4 (when R1 = H), were constructed,respectively, in fair to good yields by reacting 2 with excessive Vilsmeier reagent(DMF/POCl3). A mechanism involved in the second [5 + 1] annulation step, includinga formal [5 + 1] annulation and accompanied chlorovinylation, chloroformylation,amination and aromatization reactions, is proposed.In this paper, 32 new products were synthesized and characterized via IR. 1HNMRand 13CNMR, and one dihydropyrido[2,3-d]pyrimidine was characterized byX-ray diffraction analysis. The mechanisms for the reaction of pyridine and Vilsmeierreagent (DMF/POCl3) were discussed.