Observation of a tetrahedral intermediate and its anion in a hydrolysis reaction. Ring opening of a quinazolinium ion

Abstract

The behavior of the 3,4-dihydro-1,3-dimethyl-4-0xoquinazolinium ion (Q') in basic aqueous solution (pH 7-1 4 ) has been studied. Kinetic studies afforded information about four distinct processes: (a) the relatively fast equilibration of Q' with its pseudobase QOH; (b) the slower equilibration of the manifold comprised of Q' , QOH, the pseudobase anion QO-, and the ring-opened form, a formanilide derivative, F (equilibrium is approachable starting from Q' or from F, which exists in solution as a 3:1 mixture of two atropisomers); (c) slower equilibration of the less stable atropisomer of F into the same manifold as above; and (d) hydroxide ion catalyzed hydrolysis of the formanilide moiety to give the benzamide A. The species QOH and QO-, which are observable by UV and NMR spectroscopy, are tetrahedral intermediates at the carboxylic acid level of oxidation. The present work is a rare instance where such intermediates have been observed and where analysis of the kinetic data has provided rate constants for their formation and decomposition starting from different precursors. In strongly basic solutions the equilibrium F s QO-+ H+ is displaced toward QO-; that is, the tetrahedral intermediate anion is thermodynamically stable relative to its acyl precursor. (6) (a) Patchornik, A.; Berger, A,; Katchalski, E.

Kinetics and mechanism of the bromination of phenols and phenoxide ions in aqueous solution. Diffusion-controlled rates

“…44 In the earlier work (Tables I, III, and IV)la the stored curve was plotted out onto large graph paper, digitized, and then analyzed.44 For the later studies,18 the waveform recorder was interfaced to an Apple II microcomputer. 59 In cases where the decay of transient cyclohexadienones5 interfered with the infinity readings, the monitoring wavelength was set at 275 nm.…”

“…gave 72 mg of a red solid with mp and NMR properties identical with those of quinone 13. The 13C NMR spectrum indicated that ,80 had been incorporated on C-4 and the CIMS data indicated that the product consisted of 68% of 180-labeled quinone 14 and 32% of unlabeled quinone 13: 13C NMR (Me2SO-46) & 14.60 (CH3), 25.73 (Ctf2CH2N), 38.56 (CH2N), 59.37 (OCH2), 106.31 (C-6), 119.43 (C-3), 122.65 (C-2), 123.15 (C-3a), 132.05 (C-7a), 156.11 (C02), 159.47 (C-5), 178.50 (C-7), 178.70 (C-4 of 14, rel intensity 41.6), 178.75 (C-4 of 13, rel intensity 28.8); CIMS mje (rel intensity) 279 (51.9 MH+), 281 (100.0), 282 (17.2).…”

Studies of rutaecarpine and related quinazolinocarboline alkaloids

“…The reactions are, however, not unexpectedly, rather indiscriminate and complex reaction mixtures were obtained. Only rutaecarpine and dehydrorutaecarpine (30) were identified among the array of products. In this connection it was found that 2,3-dichloro-4,5-dicyanoquinone (DDQ) in dioxane readily converted 1 into 30.27 Finally it might be added that the interaction of 19 with Hg(OAc)2 was studied already by Clauder,28 who, however, had erroneously assigned to 19 structure 21.…”

Investigations into the H-D Exchange of Malonganenone B

“…Subsequently work was done to demonstrate a tetrahedral intermediate in this hydrolysis reaction 38. Kinetics for each equilibrium in this reaction were analysed using UV and NMR spectroscopy and the mechanism they propose matches that proposed here.…”

“…The change in ratio in different solvents was puzzling, however, until now: interchange between rotamers is possible, but only through the tetrahedral intermediate 36, which can open to yield either rotamer. 38 Although bond breaking is required to interchange these, and hence they could be…”