Formation of Alkenes from Vicinal Dihalides and p-Halo Nitroalkanes by Elimination Reactions with One-electron and Two-electron Reducing Agents

Abstract

Reactions of vicinal dihalides [1a, c-f] with sodium sulfide in DMF at room temperature afforded halogen-free alkenes in good yields. Several 8-halo nitroalkanes [2a-f] were prepared and treated with sodium sulfide in DMF. β-Halo-β-(substituted phenyl)nitroalkanes [2c, d, g] gave α-haloalkenes[4c, d] or a-nitroalkene [5g]via the E 2-anti elimination mechanism. When [2 c, d, g] were allowed to react with mild reducing agents such as tin (II)chloride, amalgamated calcium, amalgamated sodium, and sodium dithionite, however, synchronous elimination of the nitro group and the halogen atom took place via the elimination radical chain (E_RC) mechanism to produce halogen- and nitrogen-free alkenes [3 c, d-f]. The reducing agents which gave [ 3] and [ 4] from 2 were found to belong to one-electron and two-electron reducing agents, respectively, generalized by Mathai et al.