Alkoxides reaction with dihalides

The current working model for the beneficial role of protic and halide additives in reactions with aliphatic amines is outlined in Scheme 9.10 [11]. In these reactions, the rhodium dihalide dimer 30 is proposed to enter two different catalytic cycles. In the productive catalytic cycle, the dimer is cleaved by solvation or binding with the substrate to give 31. Oxidative insertion followed by pro to nation of the rhodium alkoxide... 

Williamson reaction The formation of an ether by the treatment of an alkyl halide with an alkoxide anion. Gem-dihalides react with alkoxides to give acetals, while 1,1,1-trihalides give ortho esters. 

Syntheses that exploit the solubility of the alkaline-earth metals in liquid ammonia have proven practical for alkoxide work, as they generate high yields, reaction rates, and purity (Table 8, Equation (3)). In a refinement of this approach, Caulton and co-workers have used dissolved ammonia in an ethereal solvent, usually THF, to effect the production of a number of alkoxides of barium, and this method has also been examined with calcium and strontium (Table 8, Equations (4a) to (4c)). Displacement reactions using alkali metal alkoxides and alkaline-earth dihalides (Table 8, Equation (5)), and between alkaline-earth hydrides or amides and alcohols (Table 8, Equations (6) and (7)), have been examined, but alkali-metal halide impurities, incomplete reactions, and unexpected equilibria and byproducts can affect the usefulness of these approaches. 

The reactions of metal alkoxides with halogens were investigated by Nesmeyanov et al. who observed that the reaction between titanium tetra-n-butoxide and chlorine or bromine yielded the dihalide dibutoxide coordinated with one mole of alcohol as TiX2(OBu)2.BuOH and n-butyl propionate. The reaction may be represented by... 

Reactions of vinylboron dihalides with benzyloxides and propargyloxides have also been examined and they proceed quite well. Isolation of racemic products from reactions employing chiral alcohols further supports a cation pathway for the alkenyl group migration. The tandem reactions of in situ generated alkoxides with vinylboron dihalides has also been accomplished (Scheme 23.73). 

SCHEME 23.73 Tandem reactions of in situ generated alkoxides with vinylboron dihalides. 

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