Spectroscopic Studies of Keto-Enol Equilibria. VI. β-Ketoamides and β,β-Diketoamides¹

Abstract

Model compounds for the diketoamide portion of aureomycin have been investigated by both p.m.r. and infrared spectroscopy. Systems such as 2-carbamoyl-5,5-dimethylcyclohexane-l,3-dione are enolic with very strong hydrogen bonds. Some of the factors responsible are explored. Some evidence has appeared for the highly enolic character of the diketoamide grouping in tetracycline antibiotics. For example in crystal studies of aureomycin [I, R = N(CH3)2], Donohue and his collaborators2 found abnormal bond lengths in the amide function (C-2). They suggested that one of the chelated protons was at-

Contributions to the chemistry of 3‐cyanoacetylhydrazono‐2‐indolinones and X‐ray structure of Z‐3‐cyanoacetylhydrazono‐2‐indolinone monohydrate

“…In the 1 H NMR spectra of the acetylation products 4 and 5, the CH 2 signals are absent. However, because of the possibility for various chelated mesomeric or tautomeric forms [36][37][38] the signal of C(O) CH(CN) C(O) Me could not be unequivocally assigned. In the IR spectra of compounds 1-7, the CN bands show diverse intensities (Table 3).…”

Infrared absorption spectra of 2-oxo-1,3-bis-(phenylhydrazono) derivatives and related bis- and tris-phenylhydrazones

“…In a study of the infrared spectra of aminoquinones, Wallenfels and Draber [33] assigned a medium to strong band at 1509 to 1491 em-I to tural study of amidoximes in solution, recognized a NH2 (bending) absorption at 1620 to 1575 cm-I ; the bands disappeared on deuteration. Dudek and Volpp [35], in a study of the structure of /3-keto amides and /3,/3-diketo amides , observed N -H (deformation) absorption at 1642 and 1563 cm-I ; deuteration shifted the 1563 cm-I band to 1458 cm-I , indicative of chelated coupling; the authors [35] assigned the band at 1492 to 1458 cm-I to N -D (deformation).…”

“…lnterconversion of compound XI produced spec· troscopically pure tautomer II; the other members of the 2-oxo·1,3·bis(phenylhydrazones) studied, compounds I and III to VI, deviate somewhat from the pure enolic structure, analogous to la, and show (in addition to the N = N band) a minute abcorption due the hydrazono structure [C = Nand N -H (bending) absorption]. Compound XIV shows a normal carbonyl absorption at 1686 cm-I ; a displacement of normal carbonyl absorption (1700 to 1650 cm-I ) to a lower frequency (1584 cm-I ) is generally associated with a chelated C = 0 group [35]; hence, the infrared finding is in agreement with the n.m.r. spectrum of XIV, which shows the presence I)f one chelate ring between two phenylhydrazono groups [4,5].…”

Synthesis of Conjugated Enamino Compounds Inhibiting Photosynthetic Electron Transport

“…17 ) There should be also an enamine and enol-imine tautomerism as well as the methylidene derivatives. From 13C-NMR, IR and UV analyses of 22, 23, 24 and 2~, and a red-brown coloration of 24 and 25 by ferric chloride, it was deduced that the preferred lithium diisopropyl amide (LDA) produced an alkylated product (16). This alkylation caused asymmetry in the ring system of 16 to give two isomers in a one-to-one ratio, which was indicated in the NMR spectrum.…”