Stereochemical study of sodium-ammonia reduction of acyclic allenes

Abstract

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.

Selective Reduction of Amino Allenephosphonates: Preparation of α‐Amino Vinylphosphonates

“…Among these methods, reduction by hydrogenation, [24][25][26] by hydroboration, [27] with sodium in liquid ammonia, [28] or with diimide [29] have proved to be efficient. Among these methods, reduction by hydrogenation, [24][25][26] by hydroboration, [27] with sodium in liquid ammonia, [28] or with diimide [29] have proved to be efficient.…”

“…Many methods for the partial reduction of allenes to alkenes have been reported in the literature. Among these methods, reduction by hydrogenation, [24][25][26] by hydroboration, [27] with sodium in liquid ammonia, [28] or with diimide [29] have proved to be efficient. However, most of these methods suffer from poor yields and low stereoselectivities.…”

“…It has to be noted that all the methods reported here require highly functionalized starting materials that are often difficult to prepare on a large scale. Among these methods, reduction by hydrogenation, [24][25][26] by hydroboration, [27] with sodium in liquid ammonia, [28] or with diimide [29] have proved to be efficient. [21] Therefore, if we are to benefit from the advantages of the α-AVP motif, a new strategy for the synthesis of these compounds is necessary.…”

Regioselective Diboron-Mediated Semireduction of Terminal Allenes

“…With optimized conditions in hand, a series of substrates was evaluated to determine the steric and electronic effects on the semireduction procedure (Scheme 3). Electron-withdrawing substituents such as chloro were well tolerated in the ortho, meta and para positions (3)(4)(5). A fluorine atom in the ortho position is also an efficient substrate affording alkene 6 in 61% yield.…”

“…2 However, there are only a very limited number of investigations on the complementary terminal alkene reduction. Previously reported methods to achieve this transformation include sodium-ammonia, 3 diimide, 4 diisopropylaluminum hydride, 5 silyl-cupration/protodesilylation 6 and rhodium-catalyzed hydrogenation (Scheme 2b). 7 Unfortunately, these methods suffer from several limitations in-cluding severely narrow substrate scope, low stereoselectivity, poor yields and harsh reaction conditions.…”