Cyclopropanes. XXXIV. Ring enlargements and rearrangements from carbanionic .alpha. additions to isocyanides

Abstract

The reaction of 1-methyl-2,2-diphenylcyclopropyllithium (1) with 1,1,3,3-tetramethylbutyl isocyanide resulted in a ring enlargement to yield 2,2-diphenyl-4-methylcyclobutanone (2). A similar ring enlargement was observed when l-methyl-2,2-diphenylcyclopropyl isocyanide (4) was treated with lithium or sodium metal in dimethoxyethane. In this latter reaction one also obtained an equal amount of rearranged 4,4-diphenyl-2-butanone (6). Reaction of 4 with a solution of sodium in liquid ammonia produced 1,1-diphenylbutane (10) and 2methyl-4,4-diphenylpyrolidine (11). Reaction pathways leading to the formation of the ring-expanded and rearranged products are discussed.We have previously shown that the addition of lithium alkyls to isocyanides leads to the formation of lithium aldimines.2 The lithium aldimine intermediate can be used for the preparation of 1-d-aldehydes, ketones, -keto acids and esters, and a-and (3-hydroxy ketones.3 However, we found that 2,2-diphenyl-l-methylcyclopropyllithium (1) did not undergo a simple a addition to 1,1,3,3-tetrameth-

Isocyanides. Dissociation of metallo aldimines

“…Moreover, the replacement of both alkyl groups in 2phenyl-2-butyl isocyanide by two phenyl groups caused the aldimine to dissociate very rapidly (-78°, less than 15 R = 1,1,3,3-tetramethylbutyl min) largely owing to the stability of the trityl anion produced. These results are consistent with the postulate that both relief of steric strain and the formation of a stable anion are the driving forces for the dissociative ring opening of the lithium aldimine intermediate 4 obtained by the addition of 2,2-diphenyl-l-methylcyclopropyllithium to TMBI (eq 9) , 18 The effects of varying the organolithium reagent upon the reaction product composition resulting from the dissociation of metallo aldimines are given in Table V. It should be pointed out that all of the reactions are conducted under an argon atmosphere.…”

Strain‐Driven, Non‐Catalysed Ring Expansion of Silicon Heterocycles

“…Therefore, carbocycles are generally modified by introduction of substituents to enable the desired reaction [37] . These substituents can be for example fused ring systems, [37] ketones [38] or alkali metals [39] . In contrast, silacycles do not rely on the introduction of specific functional groups or substituents due to a greater polarization of the bonds in the ring system and the presence of a Lewis acidic site.…”