Triethylammonium formate, hydrogenation

The phenolic OH group can be removed by Pd-catalysed hydrogenolysis of its triflate 522 with triethylammonium formate [261]. Naphthol can be converted to naphthalene by the hydrogenolysis of its triflate. The Ni-catalysed reduction of aryl mesylates 523 is possible using MeOH and Zn as the hydrogen donor [262]. Smooth removal of phenol groups as triflates and mesylates is not possible by any other means. 

The synthetic potential of reductions by formate has been extended considerably by the use of ammonium formate with transition metal catalysts like palladium and rhodium. This forms a safe alternative to use of hydrogen. In this fashion it is possible to reduce hydrazones to hydrazines, azides and nitro groups to amines, to dehalogenate chloro-substituted aromatics, and to carry out various reductive removals of functional groups. For example, phenol triflates are selectively deoxygenated to the aromatic derivatives using triethylammonium formate as reductant and a palladium catalyst. - These recent af li-cations have been reviewed. 

Hydrogenation of itaconic acid (14) with Rh(COD)Cl2 catalyst and commercially available triethylammonium formate as hydrogen source delivers (5)-(15) in good enantiomeric excess (equation 14) with hydrogen as reductant instead of ammonium formate a 94% ee is obtained. ... 

An interesting variation on conventional catalytic hydrogenation is catalytic transfer hydrogenation, in which formic acid or formate serves as the hydrogen source. Thus, indoles are smoothly reduced (and formylated) to the corresponding A -formylindoles (equations 42 and 43). Since it is difficult to avoid formylation of the indoline, it is best to employ triethylammonium formate to maximize yields of the reduction product (equation 43). 

Bicyclic cyclopropanone aminals with a succinimido moiety as iV-substituent allow displacement of succinimide by hydrogen by heating with triethylammonium formate giving 1. A ratio 3 1 of formate to aminal gave the best results. This reduction could not be applied to bicy-clo[3,1.0]hexane or bicyclo[9.1.0]dodecane systems due to ring-opening reactions under these conditions. ... 

Asymmetric hydrogen transfer from EtOH, /-PrOH or triethylammonium formate to Z-a-acetamidocinnamic acid Z-3.32 (R = Ph, Z = COMe, R = H) or to itaconic acid 7.7 (R = H) is highly enantioselective when the catalyst is a binap-Ru complex [873, 1333] (Figure 7.14). The relationship between the absolute configuration of the saturated add and the binap ligand is the same as in the catalytic hydrogenation. However, hydrogen transfer to other a,P-unsaturated acids, such as the precursor of naproxen (7.15), is less enantioselective [1333],... 

Primary Amines.— The aromatic nitro-to-amine conversion has once again received considerable attention, " especially those reductions which offer selectivity. Thus, dodecacarbonyltri-iron on basic alumina, sodium sulphide in aqueous 1,4-dioxan, triethylammonium formate in the presence of T0% Pd-C, and hydrogenation over a platinum catalyst all effect the nitro-to-amine conversion in the presence of other functionality. Azides and hydrazines are also reduced to aromatic amines by molybdenum trichloride. ... 

Berthold et al. (2002) reported use of formate salts such as ammonium formate and triethylammonium formate as hydrogen source with N-butyl-N -methylimidazolium hexaflourophosphate, ([bmim][PF ] for catal54 ic transfer hydrogenation of different homo- or heteronuclear organic compounds at 150°C with 92-98% yield. 

A corroboration of the key role of the intermediate cation 291 is the observation of a sharp yield increase of disproportionation products 297 and 298, compared to their direct formation from salt 280 on treatment of dimer 281 with catalytic amounts of triethylammonium perchlorate, which acts as the protonating agent generating intermediate 293. The formation of unsaturated dimers 296 is possible not only by the direct hydride transfer, followed by deprotonation of dimeric salt 294 (pathway a, Scheme 16), but also by equivalent 1,5-hydrogen transfer in the ortho-quinonoid intermediate 295 formed by deprotonation of the acidic methine group in intermediate 291 (pathway b). 

In non-HBD solvents such as n-heptane, tetrachloromethane, diethyl ether, deuterio-tri-chloromethane, and dimethyl sulfoxide, tropolone transfers its proton to triethylamine to give an ion pair, which is in equilibrium with the non-associated reactants. There is no formation of a hydrogen-bonded complex between tropolone and triethylamine because of the fact that tropolone itself is intramolecularly hydrogen-bonded. The extent of the ion pair formation increases with solvent polarity. In polar HBD solvents such as ethanol, methanol, and water, this proton-transfer equilibrium is shifted completely towards the formation of triethylammonium tropolonate [171]. 

For the simplest form of such reactions, palladium on charcoal is the catalyst and aqueous formate the hydrogen donor. Interfacial transport of formate is facilitated by an organophilic counter ion, and for the present purpose a triethylammonium ion is mostly used [48, 49]. 

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