Diallenes, conjugated

The work reported by Eaton and coworkers can be summarized as reactions where an allene system in conjugation with a further unsaturated functionality reacts with carbon monoxide in the presence of an iron-carbonyl complex such as Fe(CO)5 under photochemical and thermal conditions when Fe2(CO)9 is used. When diallenes are used (X=R2C=C, Scheme 9.24), five-membered carbocyclic products are obtained [51, 52], whereas when allenyl ketones (X = O) are applied, five-membered lactones are generated [53, 54]. The use of allenylimines (X = NR) leads to five-membered lactams under these conditions [55]. 

Not surprisingly, many of the methods which can be used in the synthesis of conjugated dienes can also be applied to dimerization of allenes. Thus, the bromoallenes (61) can be smoothly dimerized, for example, by treatment with 2 equiv. of copper(I) chloride in DMF at ambient temperature to give good yields of the diallenes (62). ... 

Cycloaddition. Sulfur dioxide undergoes [4 + 2] cycloaddition with conjugated diallenes at room temperature. The reaction involves rotation of the two... 

Dihydrothiophene 1,1-dioxides from 1,3-dienes s. 6, 615 2,5-dienc-2,5-dihydro-thiophene 1,1-dioxides from conjugated diallenes s. K. Kleveland and L. Skatteb0l, Acta Chem. Scand. B 29, 827 (1975) 2,7-dihydrothiepin 1,1-dioxide ring s. W. L. Mock and J. H. McCausland, J. Org. Chem. 41, 242 (1976)... 

Conjugated diallenes can undergo a [4+1] cycloaddition with carbon monoxide in the presence of catalytic amounts of pentacarbonyliron or nonacarbonyldiiron providing 2,5-dialkylidene-substituted cyclopent-3-enones (Scheme 4-303). ... 

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