The key intermediate α-substituted α-tetralone (8) has been synthesized, either via tandem MICHAEL addition-DIECKMANN condensation reaction between dienolate and methyl crotonate in a low yield or via BARTON'S radical decarboxylation of diester (9) without 4-dimethylaminopyridine in 75% yield, and applied to the synthesis of the substituted 5, 6-dihydrobenzo[a]naphthacenequinone.