Imines diisobutylaluminum hydride

TV-aluminum imines are another example of masked inline derivatives of ammonia. They are easily synthesized by partial reduction of nitriles with diisobutylaluminum hydride (D1BAL-H)6. Addition of lithium organic reagents to /V-aluminum iniines 7 derived from O-protected cyanohydrins 6 provides a-amino alcohols 8a and 8b in moderate yields and low to good diastereo-selectivities n 12. 

Another useful approach to aldehydes is by partial reduction of nitriles to imines. The reduction stops at the imine stage because of the low electrophilicity of the deprotonated imine intermediate. The imines are then hydrolyzed to the aldehyde. Diisobutylaluminum hydride seems to be the best reagent for this purpose.88,89... 

Another approach to the lycorane skeleton involving an intramolecular Diels-Alder reaction commenced with the conversion of the unsaturated nitrile 138 to the imine 139 by sequential reduction with diisobutylaluminum hydride followed by condensation with but-3-enylamine (Scheme 13) (118). When 139 was acy-lated with chloroethyl chloroformate in the presence of Hiinig base and the resulting dienamide heated at 140°C, the bicyclic carbamate 141 was isolated. If it is assumed that the Diels-Alder reaction proceeded via an exo transition state,... 

A number of functionalized 1-trimethylsilylcyclopropanes have become readily accessible along this and other routes 86). Among them, the 1-trimethylsilylcyclo-propane carboxaldehyde 156 was obtained from the spiroalkylation of trimethyl-silylacetonitrile 154 upon successive treatment with 1 equivalent of lithium diiso-propylamide (LDA), 1.5 equivalent of 1,2-dibromoethane and finally with a second equivalent of LDA. Subsequent diisobutylaluminum hydride (DIBAH) reduction of 155 followed by hydrolysis of the resulting imine with dilute sulfuric acid gave the aldehyde 156 in high yields, Eq. (49) 86). 

Oxime — imine. The low valent titanium reagent prepared from TiClj and diisobutylaluminum hydride (1 3) in THF reduces the oxime 1 to the very labile imine 2. Reduction of 2 to the corresponding amine with diisobutylaluminum... 

With few exceptions, organometalUcs add only once to nitriles (Section 8.6.4). Only if there is a very strong Lewis acid present to activate the anionic intermediate of the first nucleophilic attack will a second addition take place. An example of this second addition is the reduction of nitriles with LiAlH4, which proceeds all the way to the amine (Section 8.6.3). The AIH3 formed from the initial reduction acts as a Lewis acid to catalyze the second addition. This second addition can be prevented by using one equivalent of a less reactive aluminum hydride like LiAlH(OEt)3 or diisobutylaluminum hydride, [(CH3)2CHCH2l2AlH. The reactions in the acidic water workup are the reverse of imine formation (Section 10.5.2). 

Camphor imines prepared from (+ )-camphor and ( > or (R)-a-phenylethylamine have been reduced with sodium borohydride to yield exclusively the endo- and coco-product, respectively59. An imine prepared from ketopinic acid ethyl ester and benzylamine has been reduced with excess diisobutylaluminum hydride to give the e.w-amino alcohol exclusively61. 

Alkylative Beckmann rearrangements of oxime sulfonates are promoted by trialkylaluminums. The rearrangements give the imines, which are reduced with Diisobutylaluminum Hydride to the corresponding amines (eq 14). Related alkylative Beckmann fragmentations have also been reported. ... 

All manipulations were carried out using standard vacuum line and dry box techniques under inert atmospheres or vacuum. Solvents were dried over molecular sieves and stored under nitrogen. Diisobutylaluminum hydride and the nitrile reagents were used as received. CAUTION Diisobutylaluminum hydride (DIBAL-H) is very moisture sensitive in dilute solutions and pyrophoric when neat The alkylaluminum imine complexes were prepared by literature methods (41). Thermal polymerization of the aluminum imine complexes was accomplished as previously reported (42-45). Controlled headspace analysis was conducted by holding seal ... 

Diisobutylaluminum hydride (DIBAL) is known to be less reactive than LiAUL and can transfer only one hydride ion per molecule. For this reason DIBAL is commonly used for partial reduction of esters and nitriles. Addition of DIBAL to a nitrile results in the formation of an imine-aluminum complex that is decomposed, during workup, to the aldehyde (Scheme 14). Cyanohydrins have to be protected during the synthesis of a-hydroxy aldehydes because dimerization and isomerization can take place. Even in the protected form special care has to be taken during synthesis (low temperatures) and workup [124,136]. 

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