Lithium aluminium hydride: chemoselective

We shall use this synthesis as a basis for discussion on chemoselectivity in reductions. In the first step, sodium borohydride leaves the black carbonyl group of the ester untouched while it reduces the ketone (in yellow) in the last step, lithium aluminium hydride reduces the ester (in black). These chemoselectivities are typical of these two most commonly used reducing agents borohydride can usually be relied upon to reduce an aldehyde or a ketone in the presence of an ester, while lithium aluminium hydride will reduce almost any carbonyl group. 

A few papers have reported the use of various aluminium-based reducing agents in phosphine synthesis. Lithium aluminium hydride reduction of phosphine oxide precursors provides a route to new 2-phosphinomethyl-1/7-pyrroles and diisobutylaluminium hydride (DIBAL) has been found to be an excellent reagent for the reduction of phosphinites, phosphinates and chlorophosphines. 2-Chloroethylphosphine (CICH2CH2PH2) has been prepared for the first time by a chemoselective reduction of diethyl 2-chloroethylphosphonate with dichloroalane (HAICI2), prepared in situ from LiAlH4 and AlCls. A patent has described the use of metallic aluminium... 

Lithium aluminium hydride modified with some chiral 1,2-aminodiols, for example (106), gives enantiomeric excesses of up to 82% in the reduction of aromatic ketones," and lithium tris[(3-ethyl-3-pentyl)oxy]aluminium hydride has been introduced as a chemoselective reagent (98—100%) for the reduction of aldehydes in the presence of ketones." Finally, the reagents AlCL-EtSH and AlBrs-EtSH have found further application in the cleavage of esters and lactones. 

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