Phosphides and arsenides as metal–halogen exchange reagents. Part 1. Dehalogenation of aliphatic dihalides

Abstract

Lithium diphenylphosphide and arsenide have been investigated as reagents for metal–halogen exchange. Reactions involving two molar equivalents of the anions with 1,2-dibromoethylenes lead to moderate to good yields of acetylenes and smaller yields of phosphorus-containing by-products. Similar reactions with 2,3-dichlorobuta-1,3-diene and 2-chlorobuta-1,3-diene give S_N2′ rather than direct substitution products. Evidence is presented that adamantene is an initial product in the reaction of lithium diphenylphosphide with 1,2-di-iodo- and 1,2-dibromo-adamantane, but not with 1,2-dichloroadamantane, although 1- and 2-adamantyldiphenylphosphine oxides are formed in every case. Finally reactions of phosphide anion with geminal dihalides were briefly investigated; 1,1-dibromo-2,2-diphenylethylene gave diphenylacetylene as the major product.