Kinetic study on debromination of vic-dibromides with trivalent phosphoruscompounds

Various types of trivalent phosphorus compounds (1) brought about reductive debromination of vic-dibromides (2) to afford olefins. The reaction M,as a ccelerated by either electron-releasing substituents on the phosphorus of 1 or electron-withdrawing substituents on the alpha -carbon of 2. The substi tuent effects, along With the stereochemistry of the reaction, are consiste nt 1 vith an E1CB-like mechanism for the elimination of the two bromine ato ms. That is, 1 initially undergoes nucleophilic attack upon a bromine of 2. At the transition scale, a fractional positive charge is developed on the phosphorus of 1 and a fractional negative charge on the carbon of 2. This m echanism suggests the importance of an electronic character of the vic-dibr omide in determining the relative ease of bromophilicity, carbophilicity, a nd basicity of the phosphorus of a trivalent phosphorus compound in a react ion with the dibromide. (C) 2001 John Wiley & Sons, Inc.