Aluminum alkynides alkylation

The low acidity of 1-alkynes means that strong bases must be used to form the alkynide ions and that water is not a suitable solvent aqueous solutions have a very low concentration of alkynide ions. Some transition metal alkynides can be prepared by precipitation from aqueous solution because their solubilities are very low. Suitable solvents for the preparation of alkynide ions must be less acidic than the alkyne, and preferably allow the alkyne and the alkynide ion to remain in solution. Liquid ammonia, te-trahydrofuran, ether and hydrocarbons have all been used, particularly the first, the alkynide anion being readily formed by metal amides. Alkynides of many types have been prepared from various metals. Besides Groups I and III, copper(I), silver, gold(I), zinc, mercury and, more recently, aluminum alkynides have been synthesized. The alkynides of Groups I and II have been principally used as nucleophiles in alkylation reactions, but there are now many examples of other metal alkynides in this role. Palladium-catalyzed reactions, as remarked above, have become increasingly important for the reactions of alkynides of metals other than Groups I and II, but these have not usually involved alkylation. 

One of the characteristic features of this approach is the successful fert-alkyl-al-kynyl coupling with dialkylaluminum alkynides which enables the introduction of a quaternary carbon in a position adjacent to an alkynyl group. Such transformation was previously achieved by the cross-coupling of ferf-alkyl chlorides with trialkynyl-aluminums as already described in this section [92]. The reaction of 98 with dimethyl-aluminum phenylacetylide (1.5 equiv.), readily prepared from lithium phenylacetylide and Me2AlCl, in toluene at -78 °C for 30 min resulted in formation of a cross-coupling product in 70 % yield. This result indicates the efficient and selective transfer of the alkynyl group from the aluminum center in dialkylaluminum alkynides as depicted in Sch. 65. 

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