Reductions of Cyclic 1,3-Butadiynes

Hydrogenations of 2(n)-6(n) yielded the fully hydrogenated ring systems [25]. The same holds for the macrocydic systems 67 and 81-83 (Chart 7.5) [66]. 

More interesting are reactions of compounds in which the two 1,3-butadiyne units are oriented in close proximity. Although the systems 84 and 89 do not 

The hydrogenation of 84 was carried out over Pd/charcoal to yield 86 as main product in which both 1,3-butadiyne units were converted into tetramethylene moieties. The second major product was assigned to 87 [67]. It is interesting to note that 88 was the only detectable product of the Pd-induced dehydrogenation of 86 at 320 °C. The Na/NHj reduction of 84 yielded as main product 85 and as minor products 86 and 87 [67]. Hydrogenation of 89 in EtOAc and AcOH over a Pt catalyst afforded about equal amounts of 90 and 91 [68]. 

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