Hydride transfer ammonium formate

It has been postulated that direct hydride transfer from the formate ion to the ketone does not occur, but that interaction of the quaternary ammonium formate with... 

Sodium or ammonium formates are also suitable as hydride donors for the hydrogenation of a, 0-unsaturated and aromatic aldehydes with water-soluble Ru complexes [88, 93], With [RuCl2(TPPMS)2], both the catalyst and the formate are in the aqueous phase the phase-transfer problem associated with catalysts not soluble in water and aqueous formate solutions does not arise [93, 94]. These systems olfer interesting theoretical aspects [87, 95, 186]. 

As will be discussed in the next section, 1,5-pentanediones are obtained by Michael addition of acetophenones to chalcones. The addition and cyclization may be merged in one step (see Section II,C,2,g). When acetophenone was condensed with chalcone (74) in the presence of BFg-EtaO or of HC104, jS-phenylpropio-phenone (76) was obtained as by-product its formation is due to hydride transfer to the conjugate acid of chalcone (75), which is the acceptor (experimental data and theoretical calculations show that chalcones are protonated at the oxygen atom). Balaban obtained a 72% yield in the conversion 70 -> 37 using as acceptor chalcone and as catalysts perchloric or sulfuric acids (i.e., 75). The formation of j8-phenylpropiophenone (76) in the Chichibabin synthesis of pyridines from chalcones and ketones in the presence of ammonium acetate, and in the pyrimidine synthesis from chalcones and amidines is undoubtedly due to a similar hydride transfer. 

Hydride ion transfer from formic acid and its salts finds widespread application in the reduction of organic substrates, but limited use has been made of the procedure under phase-transfer catalytic conditions. However in the presence of a ruthenium complex catalyst, it is possible to selectively reduce the C=C bonds of conjugated ketones with sodium formate [11], The rate of reduction is fastest with tetrahexyl-ammonium hydrogensulphate and Aliquat the complete reduction of chalcone being effected within one hour, whereas with benzyltriethylammonium chloride only ca. 15% reduction is observed after two hours under similar conditions. 

A valuable part of the [2,3]-sigmatropic rearrangement of ammonium ylides is the fact that stereochemical information can be transferred. For example, Kaiser and co-workers stereoselectively alkylated the C-6 position of penicillin using the nitrogen ylide 46 derived from lactam 45.28 Quatemization of 45 with allyl bromide followed by ylide generation using sodium hydride effected the [2,3]-rearrangement. This resulted in the exclusive formation of P-lactam 47 in 75% yield. 

NADH directly transfers a hydride ion to flavins and analogs (e.g., deazaflavin), indicating hydrogen transfer within a molecular complex (Scheme 7.2.27). Hydrophobic NADH derivatives with an ammonium side chain have been bound to a PEG substituent of a flavin and are then oxidized much faster to NAD than without complex formation. Chiral deazaflavino-... 

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