Synthesis of Dihydrobenzoindazoles and Dihydrobenzoquinazolines

Significance

An efficient method for the synthesis of 4,5-dihydrobenzo[g]indazoles and 5,6-dihydro[h]quinazolines via a key intramolecular Friedel-Crafts reaction which takes advantage of fluoro stabilization of incipient carbocations is reported. The reaction is triggered by Lewis acidic silicon reagents and is carried out under mild conditions in HFIP. The resulting 4-fluorinated 3-acyl-1,2-dihydronaphthalenes, upon treatment with hydrazines or amidines, undergo well-established cyclization reactions to the benzoindazoles and benzoquinazolines, respectively, in excellent yields. However, the scope of the reaction was insufficiently explored.