1.3- Dienes allenes, 3-component synthesi

Allenes are a class of compounds with unique reactivity due to the presence of the cumulated diene unit, which also makes the chirality of allenes [1]. For a long period of time, this class of compounds has been considered as very unstable [2]. In reality allenes are not so unstable recent observations have shown that allenes possess good reactivity and selectivity in organic synthesis [3]. Since some of the most recent advances in the chemistry of allenes have been summarized in several reviews and accounts, this chapter will summarize the typical advances in Pd-catalyzed two- or three-component cyclization of functionalized allenes, which have not been included in these reviews and accounts [3]. 

Grigg et al. reported a successful four-component domino reaction for the synthesis of functionalized dienes 316 from aryl iodides, allyl amine derivative, allene, and carbon monoxide [110] (Scheme 6.83). Carbon monoxide could insert into the C—Pd bond of arylpalladium(II) iodides to generate a carbonylpalladium species, which is followed by allenylation to form n-allylpalladium species. Finally, the attack of the nitrogen nucleophile produces the product observed. The products of this domino multicomponent reaction could be subjected efficiently to ring-closing metathesis in the presence of Grubbs second-generation catalyst. 

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