Enols of 2‐nitro‐ and related 2‐substituted malonamides

Abstract

The structures of 2‐substituted malonamides, YCH(CONR1R2)CONR3R4 (Y = Br, SO2Me, CONH2, COMe, and NO2) were investigated. When Y = Br, R1R2 = R3R4 = HEt; Y = SO2Me, R1–R4 = H and for Y = CONH2 or CONHPh, R1–R4 = Me, the structure in solution is that of the amide tautomer. X‐ray crystallography shows solid‐state amide structures for Y = SO2Me or CONH2, R1–R4 = H. Nitromalonamide displays an enol structure in the solid state with a strong hydrogen bond (O…O distance = 2.3730 Å at 100 K) and d(OH) ≠ d(O…H). An apparently symmetric enol was observed in solution, even in appreciable percentages in highly polar solvents such as DMSO‐d6, but Kenol values decrease on increasing the solvent polarity. The N,N′‐dimethyl derivative is less enolic. Acetylmalonamides display a mixture of enol on the acetyl group and amide in non‐polar solvents, and only the amide in DMSO‐d6. DFT calculations gave the following order of pKenol values for Y: H > CONH2 > COMe ≥ COMe (on acetyl) ≥ MeSO2 > CN > NO2 in the gas phase, CHCl3, and DMSO. The enol on the CO group is preferred to the aci‐nitro compound, and the NOH…OC is less favored than the COH…OC hydrogen bond. Copyright © 2009 John Wiley & Sons, Ltd.

A Rich Array of Reactions of Cyanomonothiocarbonylmalonamides RNHCSCH(CN)CONHR‘ and Their Thioenols RNHC(SH)C(CN)CONHR‘1

“…The ORTEPs and the full crystallographic data for the three compounds are given in the Supporting Information. A similar reaction, giving products 16 with different R 3 −R 5 substituents in the presence of a catalytic amount of p -toluenesulfonic acid, was reported by Vovk and co-workers at about the same time of our preliminary report . None of the products 16b − p are identical with those reported by Vovk.…”

“…In recent years, we prepared many enols of carboxylic acid amides Y‘YCC(OH)NRR‘ (Y, Y‘ = electron-withdrawing groups, EWGs) 1 and/or their tautomeric amides Y‘YCHCONRR‘ 2 and studied their properties, including the equilibrium constants K Enol between the two tautomers. , Initial studies on their functionalization included reactions with diazomethane, an intramolecular cyclization of derivatives prepared analogously to the formation of 1 and 2 , and their oxa-ene reactions with 4-phenyl-1,2,4-triazoline-3,5-dione . Fewer thio analogues of these species are known, , and an extensive series of “formal” 8 cyanomonothiocarbonylmalonamides 4 were isolated .…”

Quasi-aromaticity—what does it mean?

“…Recently, several enols of 2-substituted malonamides were subjected to structural investigations revealing the presence of a strong hydrogen bond responsible for structure stabilization. 160 Similar mechanism involving the presence of quasi-aromatic moiety was postulated for halogenations of ethyl cyanoacetate (Fig. 25).…”

The low KEnol values of β-sulfonyl-substituted amides

“…Anal. Calcd for C 14 A similar procedure was used for the preparation of compounds 5l/6l and 5n/6n. Their NMR and analytical data are given in Tables S1, S2 and S11 of Supporting Information.…”