Organoaluminums isomerization

The 3.8-nonadienoate 91, obtained by dimerization-carbonylation, has been converted into several natural products. The synthesis of brevicomin is described in Chapter 3, Section 2.3. Another royal jelly acid [2-decenedioic acid (149)] was prepared by cobalt carbonyl-catalyzed carbonylation of the terminal double bond, followed by isomerization of the double bond to the conjugated position to afford 149[122], Hexadecane-2,15-dione (150) can be prepared by Pd-catalyzed oxidation of the terminal double bond, hydrogenation of the internal double bond, and coupling by Kolbe electrolysis. Aldol condensation mediated by an organoaluminum reagent gave the unsaturated cyclic ketone 151 in 65% yield. Finally, the reduction of 151 afforded muscone (152)[123]. n-Octanol is produced commercially as described beforc[32]. 

Early attempts by Asinger to enlarge the scope of hydroalumination by the use of transition metal catalysts included the conversion of mixtures of isomeric linear alkenes into linear alcohols by hydroalumination with BU3AI or BU2AIH at temperatures as high as 110°C and subsequent oxidation of the formed organoaluminum compounds [12]. Simple transition metal salts were used as catalysts, including tita-nium(IV) and zirconium(IV) chlorides and oxochlorides. The role of the transition metal in these reactions is likely limited to the isomerization of internal alkenes to terminal ones since no catalyst is required for the hydroalumination of a terminal alkene under these reaction conditions. 

Indirect evidence for this conclusion lies in the fact that as the alkylating/reducing power of the organoaluminum is increased, the extent of olefin double-bond isomerization accompanying disproportionation... 

Aldol condensation of methyl ketones. This reagent in combination with pyridine has been used to effect aldol condensation of methyl ketones by way of an organoaluminum enolate, as formulated for the aldol condensation of 2-octanone (2) to give a mixture of the isomeric C,6-ketones 3. 

The salient feature of the synthesis is the organoaluminum-promoted stereospecific pinacol-type 1,2-rearrangement common to both segments. The 338—>339 rearrangement (Scheme 46) proceeds with preservation of alkene geometry, and is completely enantiospecific. The other 1,2-rearrangement, 345 —> 346 (Scheme 47), also proceeds with no EjZ isomerization of the olefin and with complete enantiospecificity. 

Yasuda A, Tanaka S, Oshima K, Yamamoto H, Nozaki H (1974) Organoaluminum reagents of type R R NAlEt which allow regiospecific isomerization of epoxides to allylic alcohols. J Am Chem Soc 96 6513-6514... 

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