An efficient synthesis of 2-vinylic cyclic 1,3-alkadienes via the CpRu(II)- catalyzed intermolecular coupling reactions of alkynes and cyclic allenes

摘要

2-Vinylic cyclic 1,3-alkadienes can be obtained with moderate to good yields via the CpRuCl(PPh.3)2-catalyzed coupling reaction of alkynes with cyclic allenes.rn2-Vinylic cyclic 1,3-alkadienes are a class of important building block because it may participate in a variety of tandem carbon-carbon bond-forming processes, such as sequential Diels-Alder reactions. On the other hand, allenes have shown unique reactivity and stereoselectivity and become an important class of starting materials for modern organic synthesis. Recently, different types of intramolecular cyclometallation reactions of allenes with unsaturated compounds in the presence of different metallic catalysts have been studied. Trost et al. have reported the intermolecular reactions of alkenes with alkynes or allenes with α,β-unsaturated enones9 for the synthesis of 1,4-dienes and 3-methylene-4-alkenyl ketones, respectively (eqn a and b, Scheme 1). In search of a new type of reaction between allenes and alkynes, herein we wish to report our recent observations on the CpRuCl(PPh_3)_2-catalyzed reaction of cyclic allenes with terminal alkynes, which afforded 2-vinylic cyclic 1,3-alkadienes with atom economy (eqn c, Scheme 1).