Esters dihaloalkane reagents

The reactions of lithiophosphide reagents with alkyl halides or sulphonate esters have continued to find wide application in the synthesis of new phosphines. A series of phosphino-ethers, e.g., (22), has been prepared from the reactions of chloromethyl-substituted ethers with lithium diphenylphosphide. " A one-step synthesis of macrocyclic phosphino-ethers and -thioethers (23) is afforded by the reactions of dilithio-organophosphides with bis(j8-chloroethyl)-ethers and -thioethers derived from ethane-1,2-diol and ethane-1,2-dithiol, respectively. " A new family of water soluble phosphonio-phosphine ligands (24) has been prepared by the reaction of a,o)-dihaloalkanes with one mole of lithium diphenylphosphide, followed by quatemisation of the intermediate w-haloalkylphosphine with trimethylphosphine. The new ligand system (25) has been prepared by the reaction of chloromethylbenzene-chromium tricarbonyl with... 

On the other hand, it is not necessary to prepare such unstable gem-dihaloalkanes in advance. Esters can be alkylidenated by treatment with Zn-CH3CHBr2-TiCl4-TMEDA (Scheme 5.18) [15]. This reaction requires a large excess of the reagent. It should be noted that the zinc powder used in these procedures was also pyrometallurgy grade zinc, containing about 0.04-0.07% of lead. 

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