Chemical and electrochemical reduction of some pyrazolo[1,5-a]pyrimidines

Various pyrazolo[1,5-a]pyrimidines 1 are prepared by two different ways. Their chemical reduction by sodium borohydride leads generally to 4,5,6,7-tetrahydro compounds 3, while lithium aluminum hydride yields 4,7-dihydro derivatives 2 at room temperature, and 3 in refluxing tetrahydrofuran. A complex mixture of oxidizable hydrodimers is obtained by electrochemical reduction. An electroreduction at a more negative potential also gives 4,7-dihydro compounds 2. A new 4,5-dihydropyrazolo[1,5-a]pyrimidine has been obtained by condensation of 5-amino-3-methyl-1H-pyrazole with acetophenone.