Hydroalumination enantioselective nickel-catalyzed

The catalyst efficiency of these hydroalumination varies from a turnover number (TON) of 20-91. It is possible that the catalyst is deactivated by the presence of oxygen and water. Examination of the 31P NMR spectrum of the catalyst indicates that the phosphine monoxide and dioxide are formed in the presence of nickel prior to the addition of the substrate. Rigorous exclusion of oxygen and water is necessary in all these reactions. The enantioselective nickel-catalyzed hydroalumination route to dihydronaphthalenols may prove to be particularly important. Only one other method has been reported for the enantioselective syntheses of these compounds microbial oxidation of dihydronaphthalene by Pseudomonas putida UV4 generates the dihydronaphthalenol in 60% yield and >95% ee.1... 

Lautens has spearheaded the study of a range of metal-catalyzed methods for the desymmetrization of various meso-oxabicyclooctanes [40]. In initial work, enantioselective nickel-catalyzed hydroalumination reactions of substrates such as 148 proved effective for the generation of cycloheptene 150 (95% ee, Scheme 14.24) [118], as also described in Section 7.5. The related desymmetrization reactions could be effected with carbon nucleophiles as well [119, 120], Thus, asymmetric ring-opening of 145 with Me2Zn mediated by a palladium catalyst prepared in situ with ligand 146 [121] led to the C3-C9 fragment (147) of the polyether antibiotic ionomycin (151) [120]. 

The asymmetric nickel-catalyzed hydroalumination of prochiral terminal alkenes using adducts of BujAl and chiral amines was reported in 1981 [74], Among the different amines investigated, (-)-N,N-dimethylmenthylamine (DMMA) gave the best enantioselectivities. For example, reaction of 2,3,3-trimethyl-l-butene (39) at room temperature with 0.33 equiv. of the DMMA/iBu3Al adduct in the presence of 0.6 mol% of Ni(mesal)2 gave, after oxidation of the intermediate organoaluminum compounds, 2,3,3-trimethyl-l-butanol 40 in 76% yield and 27% ee (Scheme 2-19). 

The mechanism for this nickel-catalyzed enantioselective hydroalumination was initially thought to proceed via a nickel-catalyzed hydroalumination followed by the elimination of the organoaluminum with cleavage of the oxygen bridge. However, this seems unlikely in the light of recent evidence (Scheme 11). 

An enantioselective hydroalumination of a prochiral olefin was first reported by GiacomeUi and coworkers. The authors surveyed a number of chiral amines in the nickel catalyzed hydroalumination of 1,1-disubstituted alkenes. Of the amines examined, N,N-dimethylmenthylamine (DMMA) in combination with triisobutylalane and catalytic amounts of Ni(mesal)2 (mesal = methylsaHcyHde-neimine) (5) effected the hydroalumination of 2,3,3-trimethylbutene which, fol-... 

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