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The 3,4-dihydro-2-(dimethylaminomethylene)-1(2H)-naphthalenone starting material was prepared by heating a mixture of α-tetralone (5.85 g, 40 mmol) and N,N-dimethylformamide dimethyl acetal (32 ml, 240 mmol) at 110° for 3 h. The reaction was allowed to cool to room temperature and excess reagent removed in vacuo to give a thick oil. This crude material was subjected to column chromatography (silica, 5% methanol in CH2Cl2) to afford the desired product as a thick orange oil (3.50 g). δH (CDCl3) 8.02 (1 H, dd, J 7.7, 1.5 Hz), 7.72 (1 H, s), 7.36 (1 H, td, J 7.3, 1.6 Hz), 7.28 (1H, td, J 7.6, 1.5 Hz), 7.15 (1H, dm, J 7.3 Hz), 3.12 (6H, s) and 2.98-2.80 (4H, m). MS (ES+) 202 (MH+, 90%), 175 (MH+−HCN, 100%).

1. temperatureby heating
2. customexcess reagent removed in vacuo
3. customto give a thick oil