Sodium aluminohydride

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. 

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). 

Other reducing agents that have been reported to afford enamines are sodium hydrosulfite [142], dialkyl aluminohydrides [143], and Grignard reagents [144] for quaternary isoquinoline salts sodium borohydrides [145] and Grignard reagents for 3,5-dicyanopyridines and electroreduction [146, 147] of iV-methylglutarimide. 

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. 

Metal alkyl and aryl oxyhydrides are similar to alkoxides in that they involve a metal hydride attached to the oxygen from an alkyl or aryl alcohol. Examples include the aluminium metal hydride sodium bis(2-methoxyethoxy) aluminohydride and lithium aluminium-tri-tert-butoxyhydride. They are dangerous fire risks in contact with water and can decompose to evolve hydrogen gas. 

Sodium N,N-bis-2-hydroxyethyl glycinate. See Sodium dihydroxyethylglycinate Sodium bis(2-methoxyethoxy) aluminohydride. See Sodium bis (2-methoxyethoxy) aluminum hydride... 

CAS 22722-98-1 EINECS/ELINCS 245-178-2 Synonyms Sodium bis(2-methoxyethoxy) aluminohydride Sodium dihydrobis(2-methoxyethoxy) aluminate Classification Organometallic metal hydride Empirical C6Hi6AINa04 Formula Na[H2AI(0C2H40CH3L 2]... 

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