Alkenes from organoaluminums

In all of the above processes, the organoaluminum compounds serve as cocatalysts that activate a transition metal for the desired organic transformations. There are several important processes that do not involve transition metals and in which the organoaluminum reagents acts as a catalyst or stoichiometric reagent. The two most important of these are the formation of fatty alcohols and terminal alkenes from ethylene. These capitalize on the Aufbau reaction for formation of alkyl chains that can reach to C200, but the commercially important alkyls are those from C14 to C20 Oxidation of the aluminum alkyl followed by acidic hydrolysis yields predominately C14 to C20 alcohols and alumina (equation 36). The alcohols are converted to... 

Chloral. Yamamoto has found that the organoaluminum reagent prepared from MeaAl and (/ )-(+)-3,3 -bis(triphenylsilyl)binaphthol catalyzes the ene reaction of chloral and pentafluorobenzaldehyde with 1,1-disubstituted alkenes at -78 °C, giving the expected ene adducts in 40-90% yield and 60-90% enantiomeric excess. Use of the sterically hindered chiral auxiliary is necessary. Low yields of racemic products are obtained with 3,3 -diphenylbinaphthol. 

Transmetalation. Carr and Schwartz have found that an organic group bound to zirconium can be transferred to aluminum. Thus reaction of 1, obtained by hydrozirconation of alkenes or alkynes, with AlCln results in a color change from bright yellow to orange as an organoaluminum dichloride is formed. On addition of an acid chloride, a ketone (2) is formed rapidly. This new ketone synthesis proceeds in high yield from alkyl- and alkenylaluminum dichlorides. 

The hydroalumination of oxabicyclic alkenes has been developed as a novel enantioselective entry to cycloalkenols (Scheme 3-86). " Catalysts derived from Ni(cod)2 and BINAP efficiently catalyze the asymmetric hydroalumination of DIBAL-H to various oxabicyclic alkenes. Initial alkene hydroalumination is followed by ring opening of the intermediate organoaluminum to produce cyclohexenol or cycloheptenol products. 

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