Alanal, reaction with

Scheme 4.10 gives some examples of application of alkyne carboalumination in synthesis. The reaction in Entry 1 was carried out as part of a synthesis of the immunosuppressant drug FK-506. The vinyl alane was subsequently transmetallated to a cuprate reagent (see Chapter 8). In Entry 2, the vinyl alane was used as a nucleophile for opening an epoxide ring and extending the carbon chain by two atoms. In Entries 3 to 5, the vinyl alane adducts were converted to vinyl iodides. In Entry 6, the vinyl alane was converted to an ate reagent prior to reaction with formaldehyde. 

The electrophilicity of alane is the basis for its selective reaction with the amide group. Alane is also useful for reducing azetidinones to azetidines. Most nucleophilic hydride reducing agents lead to ring-opened products. DiBAlH, A1H2C1, and A1HC12 can also reduce azetinones to azetidines.100... 

Generally, during the first step, a diethyl ether adduct of the alane is synthesized, which should not be isolated and can be used for the next step (Eq. 2) in situ . This method to generate the alane has the advantage with respect to other procedures to start from the easily available lithium alanate (which should be purified before use). The reaction with the alcohol or silanol can be followed by the evolution of gaseous hydrogen. Depending on the acidity of the alcohol or the silanol the reaction mixture has to be cooled. 

We have shown that alanes substituted with alkoxy and siloxy ligands can be used very efficiently in CVD processes, either producing single ceramic phases or mixtures of several phases using only one single precursor molecule. As the processes discussed above are driven by chemical reactions within distinct molecules or in between two molecules, the phases formed are... 

Alanes, in Ru and Os half-sandwich complexes, 6, 497 Alcohol-activated reactions, with allylic tins, 9, 358 Alcohol compounds... 

The disilyl derivative of all-cix-1,2-epoxycyclopentane-3,5-diol 5 7 was treated with diethyloctynylalane to afford after cleavage of the silylether function the triol 58. This triol was convered via the acetonide to the benzyl ether 59. Hydrolysis with aqueous trifluoroacetic acid yielded the diol benzylether 60 which could be prepared by an alternative route as well. This route proceeds via the monotrityl epoxide 61 and benzylation to the trityl benzylether 62 and then reaction with diethyl octynyl alane to the diolbenzylether 60 and the isomeric 1,3-diol. 

C-Glycosides. Glycosyl fluorides react with a number of nucleophiles to provide C-glycosides. Lewis acid catalysts are not essential for reaction with A1(CH,), or A1(CH,),CN, but MgBr, is useful in reactions with Michael acceptors such as CH,=CHCN. The products are reduced by alane to tetrahydropyranes. They also react with S- and N-nucleophiles to afford the corresponding glycosides. 

Heterosubstituted 1,3-dienes. Some alkenylmetals substituted by OR, SR, or SiR, can be coupled with alkenyl halides (or aryl halides) in the presence of this Pd(0) catalyst. Alkenylzinc reagents, prepared by reaction of alkenyllithiums with ZnCh, and alkenyl-alanes are the most useful. Yields from reactions with organoboronates are low. 

Other combinations of hydrides with amides have been considered. Nakamori et al 80 83 others have looked at mixtures of Li amide with Li alanate and with Li borohydride. DFT calculations suggest that these systems will behave in a fashion similar to that of the destabilized borohydrides described above that is, the reaction products in the dehydrogenated state should have lower enthalpies than the borohydride or the alanate alone. The potential yields are higher than with LiH. For the borohydride case, the expected reaction pathway is... 

Alkali-metal hydrides, boranes or alanes react with alkoxysilanes or silanols to form Si—H bonds in reactions that often are preferred syntheses, depending on the availability of the silane reactant "Lithium hydride or alanate reductions used are ... 

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