Formamide tautomers

Benzenediamine (199) and C-(2-chloro-2-phenylacetyl)formamide (200) gave 3-phenyl-3,4-dihydro-2-quinoxalinecarboxamide (201), formulated as its 1,4-dihydro tautomer (EtOH, reflux, 6 h 56%) in contrast, the same substrate (199) with methyl C-(2-chloro-2-phenylacetyl)formate cyanohydrin (202) gave methyl 3-phenyl-2-quinoxalinecarboxylate (203), presumably by aerial oxidation of a dihydro precursor (MeCN, reflux, 12 h 7%). ... 

A -Arylimincs (21a) can be oxidatively rearranged to formamides (21b) with sodium perborate.42 The reaction works best for secondary or aryl R groups. An oxaziridinc intermediate is proposed. Results with chiral secondary R groups indicate epimeriza-tion, suggested to occur via equilibration of (21a) with its enamine tautomer. 

As far as we are aware, this type of calculation has been performed for lactim and lactam tautomers of both 2- and 4-oxopyridines [(2), (3)] and for formamide (6a) and formimidic acid (6b) only (Schlegel et al., 1982 Scanlan et al., 1983). Since the calculations mentioned are expensive, one estimates the S a b,> value by comparison of the electronic energies calculated in the HF approximation only [(HF)8EAliq)L and even this has often been done by means of semiempirical methods [(CNDO/2i8 A B,... 

Substituted 8-amino-4,5-dihydro-37f-pyrrolo[3,4-/ -l,3,5-triazepin-6-ones (51) are formed by the reaction of the formamidine (49) in an excess of aldehyde or ketone in the presence of DBU <94JCS(P1)3S71>. The intermediate product is the tautomer (50), which rearranges when dissolved in alcoholic solvents (Scheme 18). An alternative route to (51) is via the formamidate (52). 

Such processes have been studied theoretically by means of ab initio 3-2IG and 6-3IG calculations for hydrated complexes of formamide XXIa, its imidole tautomer XXIb and formamidine XXIIa [98] ... 

The NR-CAD and CAD spectra of formamide and the carbene are essentially indistinguishable, providing strong evidence that the amide and carbene tautomers retain their structures upon NR and do not undergo any rearrangements. In sharp contrast, NR-CAD and CAD spectra of the iminol ion differ markedly from each other the NR-CAD spectrum can be interpreted as a combination of the CAD spectra of genuine amide and iminol ions, in agreement with a partial tautomerization of the neutral iminol to the amide. 

Hydroxyflavone (3HF) is a widely studied molecule that undergoes an ESIPT reaction from its first excited electronic state to give a Z tautomer [19-22], In hydrogen-bonding media, H-bonded structures to the solvent molecules give normal emission at blue side of the emission spectrum. Detection of anionic forms at the Sq and Si states has been reported [23-26], Due to its extreme sensitivity to water, the effect of CD on UV-visible absorption and emission characteristics was studied in iV,iV-dimethyl formamide (DMF) [27],... 

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