A diversity oriented, microwave assisted synthesis of N-substituted 2-hydro-4-amino-pyrido[2,3-d]pyrimidin-7(8H)-ones

Developments of pyridodipyrimidine heterocycles and their biological activities

The entitled review aimed to assemble and highlight the synthetic approaches and biological aspects of heterocycles with pyridodipyrimidine motifs. The recent synthetic approaches were categorized according to the accomplishments of the approaches under catalyst or catalyst-free conditions. The topic involved the synthesis of substituted tricyclic systems and spirocyclic systems. The present study offered an overview of the recent literature in addition to a scope of the preceding literature. The proposed mechanisms of the varied target products were discussed. Pyridodipyrimidine displayed potential and privileged cytotoxic, antioxidant, and antimicrobial performances. The competitions, challenges, and prospects are also deliberated.

A captured room temperature stable Wheland intermediate as a key structure for the orthogonal decoration of 4-amino-pyrido[2,3-d]pyrimidin-7(8H)-ones

Wheland intermediates are usually unstable compounds and only a few have been isolated at very low temperatures. During our work on tyrosine kinase inhibitors, we studied the bromination of 7 in order to obtain a dibromo substituted pyrido[2,3-d]pyrimidin-7(8H)-one which could be orthogonally decorated. Surprisingly, treatment of 7 with 3 equiv. of Br2 in acetic acid (AcOH) afforded 12, a captured room temperature stable Wheland bromination intermediate stabilized by the bromination of the imino tautomer of the amino group at C4 of the pyridopyrimidine skeleton. The structure was confirmed by crystal structure determination from powder X-ray diffraction data. Treatment of 12 with DMSO afforded the dibromo substituted compound 13 presenting a bromine atom at C6 and C5-C6 unsaturation. 13 was directly accessed by treating 7 with N-bromosuccinimide (NBS), a protocol extended to other compounds using NBS or N-iodosuccinimide (NIS) to afford 6-halo substituted systems. 26, bearing an iodine at C6 and a p-bromophenylamino at C2, allows the orthogonal decoration of pyridopyrimidines.

Microwave-promoted synthesis of 3-amino-substituted 1,2-benzisoxazoles

BACKGROUND

1,2-benzisoxazole derivatives have been the focus of numerous studies, due to their biological and chemical interest.

RESULTS

We demonstrate an efficient synthesis of a series of 3-amino-substituted 1,2-benzisoxazoles from a 3-chloro-1,2-benzisoxazole by microwave-promoted nucleophilic aromatic substitution. The 3-amino-1,2-benzisoxazoles prepared were obtained in 1-6 h in good-to-high yields of 54-90%. The 3-chloro-1,2-benzisoxazoles were also prepared by heating with microwave irradiation in quantitative yields in 2 h, from the corresponding 3-hydroxy-1,2-benzisoxazoles.

CONCLUSION

This efficient microwave-assisted pathway could be applied to a variety of substrates in the further development of substituted 1,2-benzisoxazoles.