[62779-58-2] · C12H28AlLi · Lithium n-Butyl(diisobutyl)aluminum Hydride · (MW 206.28)
(reducing system for selectively converting conjugated enones and esters to allylic alcohols, esters, lactones, and acid chlorides to alcohols, acid anhydrides to alcohols and carboxylic acids, tertiary amides to aldehydes, primary, benzylic, and allylic halides to hydrocarbons, epoxides to alcohols, and disulfides to thiols)
Preparative Method: the reagent system (ate complex) is prepared and utilized in either hexane/THF or hexane/toluene solutions from equal molar quantities of Diisobutylaluminum Hydride (DIBAL) in hexane and n-Butyllithium in hexane and diluted with either THF or toluene;2a such combinations have been described as lithium trialkylaluminum hydrides, although the exact structures are unknown.2b-e
Analysis of Reagent Purity: by analysis of the reduction product of 4-t-butylcyclohexanone.2a
Handling, Storage, and Precautions: use in a fume hood; see also n-Butyllithium and Diisobutylaluminum Hydride.
This reagent system is effective for the selective 1,2-reduction of acyclic and cyclic a,b-unsaturated enones to allylic alcohols (eqs 1 and 22a and 3), particularly in hexane/toluene media.2a Small amounts (1-10%) of saturated ketones and/or saturated alcohols are observed with cyclic enones and b-phenyl enones.2a On the other hand, prior complexation of enones with Methylaluminum Bis(2,6-di-t-butyl-4-methylphenoxide) (MAD) and subsequent reduction with Li(n-Bu)(i-Bu)2AlH affords high yields of the corresponding saturated ketones resulting from 1,4-reduction (eq 3),4 except when the enone is substituted at the b position; in this case, 1,2- or a mixture of 1,2- and 1,4-reduction is obtained.4
At low temperatures (-78 °C), Li(n-Bu)(i-Bu)2AlH reduces esters, including lactones and conjugated examples, to the corresponding aldehydes and/or alcohols as mixtures (eqs 4 and 56 and 7a).2a,5-7 Often, the mixtures are further reduced with borohydride7c,d to give alcohols or oxidized to the aldehydes.5,7a,b The process appears selective for the reduction of methyl esters in the presence of t-butyl derivatives (eq 5).
Although primary and secondary amides are inert to Li(n-Bu)(i-Bu)2AlH, tertiary derivatives are reduced to mixtures of aldehydes and alcohols (eq 68a).2a,8
This reagent system reduces acid chlorides to alcohols (eq 7), anhydrides to alcohols and acids (eq 8), primary alkyl iodides to hydrocarbons (eq 9), epoxides to alcohols (eq 10) and disulfides to thiols (eq 11).2a Chemoselectivity is possible, as illustrated in eq 12.2a
MaryGail K. Hutchins
King of Prussia, PA, USA
Robert O. Hutchins
Drexel University, Philadelphia, PA, USA