Aluminohydride reductions

The reduction of simple iminium salts, as expected, occurs in an analogous way. The reduction of 39 and 40 are of particular interest since they show that attack of aluminohydride occurs from the less hindered side of the molecule (81). 

Schaeffer, G. W., J. S. Roscoe, and A. G. Stewart The Reduction of Iron(III) Chloride with Lithium Aluminohydride and Lithium Borohydride Iron(II) Borohydride. J. Amer. chem. Soc. 78, 729 (1956). 

Unlike with sodium borohydride (see Section 11.01.5.2), pyrrolizin-3-one 2 reacts with lithium aluminohydride mainly as an amide. No conjugate addition occurs, and only the reductive lactam cleavage takes place to give stereoselectively the (Z)-allylie alcohol 77. Similarly, benzo-annulated pyrrolizin-3-one 17 gives the corresponding benzylic alcohol 78. The same reactivity was observed with organometallics such as methyllithium which gives exclusively the tertiary (Z)-allylic alcohol 79 (Scheme 7). 

Reductive carbonylation of [NbCl2(PMe3)4] or reduction of [TaCl2(dmpe)2] (50) by vitride offered [NbCl(CO)3(PMe3)3] and a Ta( aluminohydride adduct, respectively (Section 34.7). 

Treatment of an ethereal solution of 4-oxo-dihydro-l,3-diaza-anthracene (108) with lithium aluminum hydride reportedly resulted in the reduction of only the 1,2-carbon-nitrogen double bond with 4-oxo-l,2,3,4-tetrahydro-l,3-diazaanthracene (109) being the only product isolated.134 Apparently conditions were not sufficiently vigorous for the further reduction of the tautomeric form of 109, or possibly the formation of a complex with the aluminohydride pre-... 

Reduction of L MNO by boro- or aluminohydrides or other reducing agents can give species with H—M—NO units that can be further reduced, for example,... 

The state of the art of reductions with metal hydrides a decade ago was the subject of comprehensive reviews. A detailed survey of reductions of carbonyl compounds with alkali and alkaline earth metal hydrides, borane and derivatives, alane and derivatives, metal borohydrides, metal aluminohydrides, silanes, stannanes and transition metal hydrides was compiled. The properties, preparation and applications of each reagent were discussed together with methods for their determination, handling techniques... 

Sodium aluminohydride (NaAlH4, SAH) in THF is somewhat less reactive than LAH toward carboxylic acids, anhydrides, epoxides, amides, and nitro compounds [CBS], and it can be used for selective reductions. However, it is as sensitive to moisture as LAH so similar precautions must be taken. 

An interesting feature of sodium bis(methoxyethoxy)aluminohydride is its solubility in aromatic hydrocarbons [Ml, MCI, W3]. It is also soluble in ethers. Most frequently, reductions are carried out in a benzene or toluene solution to which are added various cosolvents. The reaction of Red-A1 with water is less violent than that of LAH, which facilitates workup. As with LAH, hydrolysis can be carried out in acidic or basic media or with a minimal amount of water. In the last case, the addition of a small amount of acid to neutralize the NaOH that forms is recommended. 

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