Alanes optically active

Especially in the early steps of the synthesis of a complex molecule, there are plenty of examples in which epoxides are allowed to react with organometallic reagents. In particular, treatment of enantiomerically pure terminal epoxides with alkyl-, alkenyl-, or aryl-Grignard reagents in the presence of catalytic amounts of a copper salt, corresponding cuprates, or metal acetylides via alanate chemistry, provides a general route to optically active substituted alcohols useful as valuable building blocks in complex syntheses. 

Diastereoselective catalytic nitro-aldol reactions of optically active iV-phthaloyl-L-phenyl-alanal with nitromethane in the presence of LLB proceed with high diastereoselectivity (anti syn = 99 1) as shown in Eq. 3.76.125 The product is converted via the Nef reaction into (2S,3S)-3-amino-2-hydroxy-4-phenylbutanoic acid, which is a subunit of the HIV-protease inhibitor... 

Addition of alane and borane to alkenes affords a host of alkylated alanes and boranes with various reducing properties (and sometimes bizarre names) diisobutylalane (Dibal-H ) [104], 9-borabicyclo[3.3.1]nonane (9-BBN) (prepared from borane and 1,5-cyclooctadiene) [705], mono- [106,107] and diiso-pinocampheylborane (B-di-3-pinanylborane) (both prepared from borane and optically active a-pinene) [108], isopinocampheyl-9-borabicyclo[3.3.1 Jnonane alias B-3-pinanyl-9-borabicyclo[3.3.1]nonane (3-pinanyl-9-BBN) (prepared from 9-borabicyclo [3.3.1]nonane and a-pinene) [709], NB-Enanthrane prepared from 9-borabicyclo[3.3.1]nonane and nopol benzyl ether) [770] and others. ... 

Alan Baxter lost his bronze medal in the winter Olympics in 2000 because he used an American Vick inhaler and not a British one.1,2 Note the position of the CH3 attached to the central carbon atom (Figure 2.18). The British Vick inhaler contains a mixture of menthol, camphor and methyl salicylate the American Vick inhaler also contains L-methamphetamine. This is used as a decongestant and has no performance-improving properties, whereas its optically active isomer D-methamphetamine (commonly known as speed ) is a prohibited drug and is a performance improver. However, the Olympic Committee does not distinguish between these two isomers in its detective work and chemical analysis. It therefore reported that his urine contained methamphetamine and did not report that it was the ineffective l form. The committee took the medal away from him. If they only had known their chemistry and all about optically active isomers. 

Reduction Reactions of Optically Active Organosilanes by Alanes... 

The displacement reaction between triisobutylalane, complexed to certain optically active amines, and 2-alkyl- or 2-aryl-l-alkenes in the presence of /V-methylsalicylidcnc amine nick-el(Il) [Ni(mesal)2] affords optically active alkanes, upon hydrolysis of the intermediate trialkyl-alane. The chiral ligand can be recovered and recycled127. 

TABLE 24. Reduction reactions of optically active organosilanes by alanes... 

Molecular separation along with simultaneous chemical transformation has been made possible with membrane reactors [17]. The selective removal of reaction products increases conversion of product-inhibited or thermodynamically unfavourable reactions for example, in the production of ethanol from com [31]. Enzyme-based membrane reactors were first conceived 25 years ago by UF pioneer Alan Michaels [49]. Membrane biocatalytic reactors are used for hydrolytic conversion of natural polymeric materials such as starch, cellulose, proteins and for the resolution of optically active components in the pharmaceutical, agrochemical, food and chemical industries. Membrane bioreactors for water treatment were introduced earher in this chapter and are discussed in detail in Chapters 2 and 3. 

Optically active alanes have been prepared via Scheme 11. The optical purity... 

An improved procedure for the synthesis of alkyl iodides from organoboranes (and thus ultimately from alkenes), involving the use of iodine and sodium meth-oxide, has been shown to entail inversion at the C-B bond, and is employed in a new route to optically active iodides from alkenes e.g. Scheme 30). A similar sequence for conversion of alkenes to primary halides via hydrozirconation (Scheme 31) has been reviewed. Zr also catalyses addition of lithium aluminium hydride to alkenes under mild conditions, and the alanes so formed can likewise be converted into alkyl halides (Scheme 32). 

The carboalumination of terminal olefins with MeaAl in the presence of chiral zirconium catalysts [bis(l-neomenthylindenyl)zirconium dichloride, bis (l-neo- so-menthyl-4,5,6,7-tetrahydroindenyl)zirconium dichloride and so on], ZACA reaction, followed by oxidation of the chiral alanes is suitable for preparing optically active alcohols with high enantioselectivity [82] (Scheme 12). 

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