Regioselective synthesis of 2,5-dihydro-4H-pyrazolo[4,3-c]quinolin-4-ones by the cyclization of 3-acyl-4-methoxy-1-methylquinolinones with hydrazines

摘要

Reaction of 3-acyl-4-methoxy-1-methylquinolinones 2 and 5 with hydrazines has been investigated Under different experimental conditions. Compound 2 always gave rise selectively and exclusively to the regioisomeric 1,3-disubstituted- or 2,3-disubstituted-pyrazolo[4,3-c]quinolin-4(5H)one (compounds) 3a,b or 4a,b, respectively), while reaction of 5 with N-methylhydrazine led to a mixture of pyrazoles 7a and 8a. Willi N-pheny1hydrazine, compounds 7b or 8b were regioselectively obtained. Compound 8a could be selectively synthesized working ill solventless conditions. Structural educidation of all products was independently achieved by NMR spectroscopy. (C) 2008 Elsevier Ltd. All rights reserved.