Reduction of Alkynes and Cycloalkynes

61% yield of a mixture of 1,3,6- and 1,3,5-cyclooctatriene, the latter being a result of isomerization of the initially formed 1,3,6-triene [352]. 

Side reactions can be partly cut down when the reduction by alkali metals is carried out in the presence of proton donors such as triphenylmethane, fluorene, or secondary amines ( -alkyanilines). The products of the initial 

Double bonds conjugated with aromatic rings and with carbonyl, carboxyl, nitrile and other functions are readily reduced by catalytic hydrogenation and by metals. These reductions are discussed in the appropriate sections aromatics, unsaturated aldehydes and ketones, unsaturated acids, their derivatives, etc. 

The rates of hydrogenation of the double and triple bond do not differ appreciably. With some catalysts the double bond is hydrogenated even faster. This explains why it is very difficult to prevent total hydrogenation by stopping the reaction after the consumption of just one mole of hydrogen. 

Partial hydrogenation of the triple bond was achieved with catalysts over which the rate of hydrogenation decreases after the absorption of the first mole of hydrogen nickel and palladium. 

---