Decker oxidation salts

Former Results from Decker Oxidation of 3-Substituted Pyridinium Salts 3... 

The results in Table I agree with the postulated reaction mechanism. In most of cases two, isomeric pyridones 4 and 5 are formed. The structure of the N-substituent also contributes to the ratio of products, such as in the case of a series of 3-tcrt-butylpyridinium salts where the percentage of 2-pyridone decreases from 14% (N-methyl) to 0% if the N-methyl group is replaced by sterically larger and more lipophilic substituents R . Substituents like CO2H, COMe, COPh, and NOj result in the pyridone function being specifically introduced into the 6-position, so that only 5 can be obtained after Decker oxidation. Only one case (R = Me, R = CN) has been reported (7IJCS(B)131) in which traces of a 4-pyridone 6 were formed. 

This theory agrees with the later results of van Tamelen and Baran (58JA4659), who were able to get N-benzylcytisin (43) from the bicyclo-substituted pyridinium salt 42 via Decker oxidation. Since formation of an anhydro base 45 is violated according to Bredt s rule, an equilibrium between 44 and a C-6 pseudobase can exist, the latter being dehydrated to yield 43 (Scheme 9). 

However, synthesis of 6-pyridones by Decker oxidation of simple 2-alkyl-1-methylpyridinium salts was also described (54PIA(A)232 66T(Suppl 8)113). Therefore, in order to clarify the contradictory results, the oxidation of 1,2-disubstituted pyridinium salts was studied thoroughly (75AP325). 

Quinolinium salts react similarly to pyridinium compounds when oxidized. N-Alkylated salts 142, for example, yield only 2-quinolones 143 after Decker oxidation. 4-Quinolones 144 cannot be isolated (1892CB443 70HCA1903). 

As part of a synthesis program for the preparation of new antiinflammatory drugs, Pasutto et al. (85SC607) investigated the reactivity of benzo-pyrano[2,3-c]pyridinium salts 173. Upon treatment with sodium hydroxide or other nucleophiles, ring opening occurred and generated the 3-benzoylated 2-pyridones 174. In some-cases. Decker oxidation of the salts also produced the tricyclic derivatives 175 (Scheme 29). 

In a study of micelles on cyclization reactions, iV-hexadecyl-2-chloropyridinium iodide was used as an amphiphilic carboxy activating agent for lactonization and lactamization procedures (94JOC(59)415>. Ferricyanide oxidation (Decker oxidation) of 1-substituted polyarylpyridinium salts (2,4,6-triaryl, 2,3,4,6-tetraaryl, and pentaaryl) have been found to provide a general approach to synthesis of substituted pyrroles (94H(37)1347>. 

The de terated coenzyme, DPND, formed from DPN and MeCD20H in the presence of enzyme, transfers all its deuterium to Me.GHO on enzymatic reoxidation, whereas DPND formed from D2O and dithionite transfers only half of its deuterium in this process the enzymatic reduction is stereospecific but the dithionite reduction is not 3. Quaternization and Decker oxidation of nicotinamide obtained from DPND, formed by both enzymatic and dithionite reduction of DPN, gave 3-carboxamido-l-methyl-2- and -6-pyridone, both of which were still labelled (the enzymatic product half as much as the dithionite product). Thus, the quaternary nicotinamide nucleus of DPN is converted into the 1,4-dihydro form both by enzymatic and dithionite reductioni084 xhe same point was also proved for various quaternary derivatives of nicotinamide and for DPN by observing that the product of dithionite/D20 reduction could enzymatically transfer deuterium to an acceptor, whilst quaternary salts synthesized with deuterium at C(2) or G(6), and then reduced with dithionite/H20, could notions. 

The oxidation of N-alkylated pyridinium salts (1) with alkaline ferricyanide was first reported by Decker (1892CB443) and provides a standard method for the synthesis of 2-pyridones (2) (430SC(2)419). Potassium permanganate or hydrogen peroxide in alkaline solution (70T2953) as well as p-benzoquinones (63ACS2250) also perform this oxidation. However, these reagents are much less specific than ferricyanide. 

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