Studies on quinoline and isoquinoline derivatives. VIII. Hydration and hydrogenation of ethynyl substituents attached to the pyridine moiety of quinoline and isoquinoline rings.

Studies were carried out on the hydration and hydrogenation of the triple bond in quinoline and isoquinoline derivatives containing an ethynyl substituent linked directly to the pyridine moiety. Fourteen kinds of ethynyl quinolines and isoquinolines such as 2-, 3-, 4-phenylethynylquinoline, 2-, 3-, 4-(1-hexynyl) quinoline, 2-(1-propynyl) quinoline, 1-, 3-, 4-phenylethynylisoquinoline, 1-, 3-, 4-(1-hexynyl) isoquinoline, and 1-(1-propynyl)-isoquinoline were converted into the corresponding acylmethyl derivatives with high selectivity, when they were heated in dilute sulfuric acid in the presence of mercuric sulfate. In all cases, no products due to reverse hydration were isolated. Partial catalytic reduction of the ethynyl linkage of the above compounds is possible, while exhaustive reduction afforded quinolines and isoquinolines with a saturated side chain.