Novel and convenient synthesis of 1-(pyridinylmethyl)-2-naphthols and 1-(pyridinylmethylene)-2-tetralones from 2-tetralones

The reaction of 2/4-pyridine carboxaldehyes with 2-tetralone analogs in the presence of catalytic amounts of Pd/C and trimethylsilyl chloride in DMF resulted in the formation of 1-(pyridin-2/4-ylmethyl)-2-naphthols in moderate to good yields as opposed to the expected 1-(pyridin-2/4-ylmethylene)-2-tetralones. 3-Pyridine carboxaldehyde, however, formed 1-(pyridin-3-ylmethylene)-2-tetralones with 2-tetralone analogs under similar conditions. When representative reactions were repeated in the presence of anhydrous HCl gas in acetic acid, including one with 3-pyridine carboxaldehyde, 1-(pyridinylmethyl)-2-naphthols were the only products obtained with significantly improved yields. A possible mechanism explaining these results is discussed.