Substrates conjugate reduction, catalytic hydrogenation

A variety of substrates have been catalytically hydrogenated at room temperature and 1 -atm. hydrogen pressure by pentacyanocobaltate(ll) anion. Conjugation is required for the reduction of C=C bonds The effects of detailed molecular structure on reducibility and of cyanide-cobalt ratio on mode of reduction have been noted Poisoning and reactivation of the catalyst as well as the effect of alkali are described, and mechanisms are tentatively proposed for these phenomena It is concluded that the aging reaction of pentacyanocobaltate(ll) is reversible A dimerization of acrylic acids at elevated temperatures was found ... 

Amides are very weak nucleophiles, far too weak to attack alkyl halides, so they must first be converted to their conjugate bases. By this method, unsubstituted amides can be converted to N-substituted, or N-substituted to N,N-disubstituted, amides. Esters of sulfuric or sulfonic acids can also be substrates. Tertiary substrates give elimination. O-Alkylation is at times a side reaction. Both amides and sulfonamides have been alkylated under phase-transfer conditions. Lactams can be alkylated using similar procedures. Ethyl pyroglutamate (5-carboethoxy 2-pyrrolidinone) and related lactams were converted to N-alkyl derivatives via treatment with NaH (short contact time) followed by addition of the halide. 2-Pyrrolidinone derivatives can be alkylated using a similar procedure. Lactams can be reductively alkylated using aldehydes under catalytic hydrogenation... 

The influence of the solvent in a conjugate reduction can be exemplified by the synthesis of sialic add derivatives which are potent inhibitors of the influenza virus surface enzyme sialidase. " A group of potential sialidase inhibitors were obtained by the 1,4-reduction of a galacto-enonate derivative (Scheme 2). The catalytic hydrogenation of the enone substrate with 10% Pd/C in methanol afforded the 2-Ha,dai penta-acetylated... 

Some hydrogenations can be also carried out under so-called inverse PTC (IPTC) conditions where the function of a PT agent (e.g, cyclodextrin, CD) comprises the transfer of an organic substrate into aqueous phase [44]. Conjugated dienes are reduced with hydrogen to monoolefins in the presence of y9-CD and hydridopentacyanocobaltate anion, generated in situ, in alkaline aqueous solution [45], The same catalytic system is also highly effective for the IPTC reduction of the C=C bond in a,)ff-unsamrated carbonyl compounds [46]. 

Nevertheless, it must be pointed out that the formation of such transient species has never been spectroscopically observed. Native CDs are effective inverse phase-transfer catalysts for the deoxygenation of allylic alcohols, epoxydation,or oxidation " of olefins, reduction of a,/ -unsaturated acids,a-keto ester,conjugated dienes,or aryl alkyl ketones.Interestingly, chemically modified CDs like the partially 0-methylated CDs show a better catalytic activity than native CDs in numerous reactions such as the Wacker oxidation,hydrogenation of aldehydes,Suzuki cross-coupling reaction, hydroformylation, " or hydrocarboxylation of olefins. Methylated /3-CDs were also used successfully to perform substrate-selective reactions in a two-phase system. 

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