Catalysed dehydrogenation

Some companies are successfully integrating chemo- and biocatalytic transformations in multi-step syntheses. An elegant example is the Lonza nicotinamide process mentioned earlier (.see Fig. 2.34). The raw material, 2-methylpentane-1,5-diamine, is produced by hydrogenation of 2-methylglutaronitrile, a byproduct of the manufacture of nylon-6,6 intermediates by hydrocyanation of butadiene. The process involves a zeolite-catalysed cyciization in the vapour phase, followed by palladium-catalysed dehydrogenation, vapour-pha.se ammoxidation with NH3/O2 over an oxide catalyst, and, finally, enzymatic hydrolysis of a nitrile to an amide. 

The palladium catalysed dehydrogenation of benzylic alcohols was performed in molten [(C4)4N]Br without addition of base or need for oxygen (see Scheme 5.17).[74] Hydrogen gas liberated during the reaction has to be... 

Oxides and sulfides such as Cr203 and MoS2 also catalyse dehydrogenation, although only at rather high temperatures 123 they also catalyse cyclization of saturated and unsaturated aliphatic to aromatic compounds.124 Chemical methods of dehydrogenation are applicable in a large number of... 

For the sake of greater stability towards acid and chromatography the 1,13 3-tetramethyl-13-disilaisoindoline (benzostabase) protecting group was devel oped. Benzostabase derivatives are prepared by reaction of the amine with l -bis(chlorodimethylsilyl)benzene [Scheme 8.231] or l -bi (bromodimethyl-silyl)benzene or by the Pd(0)-catalysed dehydrogenative silylation of a primary amine using l,2-bis(dimethylsilyl)benzene (bp 75-80 C/1 kPa) ... 

Typical base-catalysed reactions that occur over alkali metal-exchanged zeolites include dehydrogenations, double bond isomerisations, side-chain alkylation of aromatics, conversion of methyl halides and a range of condensations. The reaction of alcohols over zeolites can be used to determine whether acid or base catalysis predominates. Whereas acid forms of zeolites catalyse dehydrations, leading to alkenes and the products of their subsequent reactions, basic sites catalyse dehydrogenations, leading to aldehydes and ketones. 

Oestreich developed a potassium tert-butoxide catalysed dehydrogenative Si-O coupling of 1°-, 2°-, and 3°-alcohols with a variety of synthetically... 

Scheme 5.10 Titanium-catalysed dehydrogenation reactions of amine-borane adducts.

Scheme 14.67 Ni-catalysed dehydrogenative cycloaddition formamides with allgrnes.

The palladium-catalysed dehydrogenation and hydrolysis of tertiary amines to aldehydes and secondary amines in good yields has been reported. 

Enzyme-catalysed dehydrogenations of this type occur frequently in metabolism. 

A mthenium(ll)-catalysed dehydrogenative coupling of saturated cyclic amines with an olefin has been reported using RuH2(CO)(PCy3)2 as catalyst under neutral conditions in THE at 70-120°C (Scheme 36) [29]. 

Catharanthine and Cleavamine. The occurrence of catharanthine is presently confined to Vinca rosea and an understanding of its chemistry was of great value in developing the structure of the antileukemic drug, vincaleukoblastine. The presence of the 15,20 double bond in catharanthine allowed a facile palladium catalysed dehydrogenation to take place at a low temperature ( 160°). This reaction may have proceeded via the intermediacy of a retro Diels-Alder product before yielding 3-ethylpyridine. When the double bond was removed a higher temperature was necessary ( 250°) and 3-raethyl-5-ethylpyridine was the isolated base. 

Harrison DJ, Edwards DR, McDonald R, Rosenberg L (2008) Toward selective functionalization of oligosilanes borane-catalysed dehydrogenative coupling of silanes with thiols. Dalton Trans 3401... 

A silver-catalysed dehydrogenative cross-coupling reaction of substituted furans, thiophene, thioazole, and pyrrole (221) with diall l phosphites... 

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