Granat D. Synthesis of pyrazolo[3,4-d]-4,5-dihydropyrimidines by [5+1] cyclization

A convenient two-step method for the synthesis of pyrazolo[3,4-d]-4,5-dihydropyrimidines (structural isomers of purines) was developed, based on reaction of aminopyrazoles and imidoyl chlorides, followed by condensation of N-pyrazolylamidines formed with carbonyl compounds. A preparative procedure for the preparation of pyrazolo[3,4-d]-4,5-dihydropyrimidines with nitrogen heterocycle annelated at the f edge is described, which can be used under combinatorial synthesis conditions. A simple two-step preparative method for the combinatorial synthesis of pyrazolo[3,4-d]-4,5-dihydropyrimidin-6-ones was developed, based on the use of commonly available reagents: amino pyrazoles, isocyanates and aromatic aldehydes. Methods for the preparation of the starting compounds for NCNCC+C synthesis of pyrazolo[3,4-d]-4,5-dihydropyrimidines, namely, (N-hetarylamino)pyrazoles, as well as pyrazoles with amidine or urea fragment at the position 5 of the heterocyclic ring, were improved.