Solid-Phase Synthesis of Pyrazolo

Scheme 10.9. Solid-phase synthesis of pyrazolo[1,5-a][1,3,5]-2-oxo-4-thioxotriazines via a...

A new solid-phase synthesis of families of asymmetrically disubstituted furazano[3,4-h]-pyrazines, which overcomes selectivity problems found in solution, has been achieved by stepwise displacement of the two chlorine atoms of 5,6-dichlorofurano[3,4-b]pyrazines with nucleophiles <02TL4741>. Pyrazolo[3,4-fe]quinoxalines as a new class of cyclin-dependent kinase inhibitors have been described <02BMC2177>. 

The solid phase parallel synthesis of tetrahydroim idazo[ 1,2-a] [ 1,3,5J tri azep i n-2-thiones and 2-imines has been reported starting from resin-bound peptides <06JCO127>. Pyrazolo[T,5 l,6]pyrimido[4,5-cfjpyridazinones with potent and selective phosphodiesterase 5 (PDEj) inhibitory activity have been described <06JMC5363>... 

We have described studies that led to the development of an efficient procedure for the synthesis of novel 7,8-functionalized pyrazolo[l,5-a][l,3,5]-2-oxo-4-thioxotriazine derivatives 8 (Scheme 10.9) and that involved solid-phase cyclization reactions of resin-bound 3,4-functionalized 5-amino-1-dithiocarboxy-pyrazoles 44 with various isocyanates." These key intermediates then serve as precursors for the target 7,8-functionalized pyrazolo[ 1,5-a][ 1,3,5]-2-oxo-4-thioxotriazines 8. 

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