The sodium-ammonia reduction of alkyl-substituted allenes (1,2-octadiene, 1,2-nonadiene, 2,3-nonadiene, 4,5nonadiene, 3-ethyl-1,2-pentadiene, and 2,4-dimethyl-2,3-pentadiene) and aryl-substituted allenes (phenylpropadiene and 3-phenyl-l,2-butadiene) has been described. Alkyl-substituted allenes were reduced smoothly to give good yields of olefins, while aryl-substituted allenes provided principally alkylbenzenes. Potential routes for the formation of these products have been investigated. Evidence has been obtained for the isomerization of allenes to internal alkynes, wherever possible, before reduction. The allenes, which are not capable of isomerization to internal alkynes, seem to undergo reduction directly.It has been shown earlier that the blue solution formed by dissolving sodium in liquid ammonia is an excellent reagent for reducing allenes to olefins.1 11This particular method of reduction, in combination with an elegant two-step synthesis of alienes,2,3 has proved to be advantageous for synthesizing a higher homolog of an olefin in good yield.Medium-sized cyclic allenes are found to yield cis olefins1,4 on reduction with sodium-ammonia. This reaction has been used recently in the synthesis of cfs,cfs-l,5-cyclononadiene1,5 and cfs,ci's-l,6-cyclodeca-diene6 because of the advantage offered in selectivity of reduction. Allenes have been proposed as intermediates in the metal-ammonia reduction of certain medium-sized cyclic acetylenes which also form cis olefins.7-9 Since some confusion exists as to the nature of the products in the reduction of acyclic alienes,1,10 we undertook a study of the reduction of representative acyclic allenes with sodium-liquid ammonia, with the intention of examining the stereospecificity of the reduction and of establishing, if possible, the potential path through which the olefins arise. Results and DiscussionFor the present investigation, we have made use of the following acyclic allenes-mono-, di-, and tetraalkyl allenes (1,2-octadiene, 1,2-nonadiene, 2,3-nonadiene, 4,5-nonadiene, 3-ethy 1-1,2-pentadiene, and 2,4-dimethyl-2,3-pentadiene), and aryl allenes (phenylpropadiene and 3-phenyl-l,2-butadiene). All of the alienes except 2,4-dimethyl-2,3-pentadiene were prepared according to the general two-step method for synthesizing alienes.2,3 They showed properties which were identical with the reported values.10-13(1) D.
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