Alkynylaluminum Reagents

Alkynylaluminum reagents have shown some promise for cross-coupling ability (Table 9.23). Owing to the considerable polarization of the Al-C(sp) bond. 

Gau et al. [352] recently used a simple Ni-based catalytic system to achieve highly efficient cross-coupling of various benzylic and aryl bromides to alkynylalanes with yields 90% in almost all cases. A more sophisticated Hgand system was used to afford the first enantioselective conjugate addition of an alkynylaluminum to 

Owing to their pronounced reactivity, alkynylindium reagents typically require short reaction times. The possibility of a stoichiometry-controUed sequential one-pot cross-coupling to 3,4-dichloromaleimides under Pd catalysis has been demonstrated [362]. A distinct chemoselectivity of triorganoindium reagents has been observed favoring replacement of bromo over chloro functionahties in 2,5-dihalopyrimidines [360]. 

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Unsaturated compounds, synthesis with alkenyl- and alkynylaluminum reagents, 32, 2... 

The regioselectivity of epoxide-opening reactions using alkynylaluminum reagents for prostaglandin synthesis has been studied by Matthews and Eickhoff [75], With two different cyclopentane oxide derivatives, they pointed out that simple substitution of an aluminum ate complex for the usual trialkylaluminum can sometimes be useful in achieving the desired regioselectivity, as observed in Sch. 46. 

Representative procedure for catalytic enantioselective addition of alkynylaluminum reagents to allylic phosphates ... 

Table 9.23 Examples of alkynylaluminum reagents in cross-couplings.

Dabrowski JA, Haeffher F, Hoveyda AH (2013) Combining NHC-Cu and Br0nsted base catalysis enantioselective allylic substitution/conjugate additions with alkynylaluminum reagents and stereospecific ismnerization of the products to trisubstituted allenes. Angew Chem Int Ed 52 7694-7699... 

Micouin et al. found that the nucleophilic substitution of bicycUc hydrazine-epoxide 7 using alkynylaluminum reagent led to the formation of hydroxy group-rearranged product 8 (Scheme 6) [20]. The plausible mechanism of this unique reaction involves (1) the initial formation of aziridinium cation intermediate catalyzed by aluminum Lewis acid and (2) the intramolecular nucleophilic migration of alkynyl group, as in transition state 9. 

Formation and Reaction of Alkynylaluminum Reagents. Lithium acetylides react with Et2AlCl to form LiCl and diethylaluminum acetylides. The aluminum acetylides are useful reagents for carrying out Sn2 reactions on epoxides (eq 8) and undergo conjugate addition to enones that can adopt an S-cis conformation (eq 9). ... 

Formation and Reaction of Alkynylaluminum Reagents. Lithium acetylides react with Me2AlCl to give dimethylaluminum acetylides that react analogously to the more commonly used diethylaluminum acetylides (see Diethylalu-minum Ethoxyacetylide). Addition of the aluminum acetylide to propiolactone results in an Sn2 reaction to give an alkynic acid (eq 1) ... 

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