Allenynes, cycloaddition

Thus far, the [5 + 2 + 1]-reaction works efficiently with alkynyl esters, amides, aldehydes, and ketones or an alkynyl-substituted allene44 as the two-carbon component (Scheme 58). Just as in the case of the [5 + 21-cycloaddition of VCPs and allenynes, the [5 + 2 + l]-reaction is selective for the allene over the alkyne subunit (Equation (35)). 

The thermal [2 + 2]-cycloaddition of allenyne 68 was used for the preparation of a naphtho[a]cyclobutene skeleton 69 [66]. 

Brummond et al. disclosed that acyclic allenynes could be efficiently converted into tetracyclic compounds via consecutive rhodium-catalyzed Alder-ene and double Diels-Alder cycloaddition reactions [47]. The former reaction transforms alkynyl allenes such as 45 into triene-ynes (46) using rhodium biscarbonyl chloride dimer. 

Scheme 11 (a) A )i -Ti Ti -acetylide bimetallic Au catalyst (24) used in the azide-alkyne cycloaddition, (b) a gem-diaurated catalyst (25) used for the cycloaddition of dialkynes, and (c) a trimetallic gold complex (26) used in the cycloisomerisation of allenynes... 

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