Synthesis of NH-, 2H-4,5-Dihydrobenz[g]inazoles and Related Compounds from 1-Tetralone Carbomethoxyhydrazones and Aromatic Esters

The carbomethoxhydrazones of 1-tetralone, 6-methoxy-1-tetralone, and 5,7-dimethyl-1-tetralone were converted to dilithiated intermediates with excess lithium diisopropylamide and condensed with aromatic esters to give C-acylated intermediates that were not usually isolated but cyclized directly with acid to afford the N-carbomethoxydihydrobenzindazoles. These compounds could be separately saponified followed by decarboxylation to the targeted NH-dihydrobenzindazoles. Single-crystal X-ray analysis for several compounds indicated that a single tautomer was present, with the NH-hydrogen atom bonded exclusively to the N-2 of the products. Theoretical calculations indicated this product to be the more stable of the two tautomers.