Oxidation hydroalumination adducts

Once the hydroalumination adducts of C=C and C C bonds have been cleanly formed, protolysis or oxidation can produce useful derivatives. With H2O or O2, generally all available C—Al bonds are destroyed. Protolysis or deuteriolysis of such adducts constitutes an overall reduction or deuteriating reduction of the original C—C unsaturation (equations 13, 39 and 41 Schemes 6-8). ° Any stereoselectivity or regioselectivity of the original hydroalumination is preserved. 

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). 

A variety of conjugated dienes can be synthesized stereospecifically via the hydroalumination of al-kynes. For example, the first-formed adduct from an alkyne can insert a second mole of alkyne and upon hydrolysis yield the ( , )-1,3-alkadiene (equation 23). Alternatively, the first-formed adduct can directly oxidatively dimerize to the ( , )-1,3-diene (equation 64). ... 

Alkenes can be converted into primary alkyl acetates via titanium-catalysed hydroalumination (Scheme 2) followed by lead tetra-acetate oxidation of the dialkyldihydroaluminate addition products (2). Only two equivalents of alkene are used per aluminium atom as it seems that only two alkyl groups from the aluminates can participate in the oxidation. In a closely related study a titanium-boron complex has been found to promote catalytic hydroboration of alkenes (also Scheme 2) cw-addition predominates for non-terminal alkenes. The adducts (3) can be oxidized to alcohols, and it may be seen that both sequences provide anti-Markovnikov products. 

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