Photodecomposition Mechanism of o-Diazonaphthoquinones Studied by Laser Flash Photolysis with Infrared Detection

Oishi, Shogo; Watanabe, Yoshihiko; Kuriyama, Yasunao

doi:10.1246/cl.1994.2187

Cited by 4 publications

(2 citation statements)

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“…Two successively formed intermediates were assigned as ketene 193 and enol 194 by means of their pHrate profiles (Scheme 29). [173] The conversion of 193 into 194 [174] and of 194 into 195 [175] was explored in some detail. Although the carbenes 191 were trapped by protic solvents with formation of 192 (9Ϫ15%, see Section 3.4.1.…”

Section: Laser Flash Photolysis (Lfp)mentioning

confidence: 99%

100 Years of the Wolff Rearrangement

2002

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The conversion of α‐diazo ketones into ketenes, and products derived therefrom, was discovered by Wolff in 1902. Major applications of the Wolff rearrangement, such as the Arndt−Eistert reaction (homologation of carboxylic acids) and the ring contraction of cyclic ketones, have been with us for some while. Nevertheless, substantial progress has been made recently. The reaction mechanism has been explored by means of matrix isolation, time‐resolved spectroscopy, and computation. Full retention of configuration of the migrating group has been established by using enantioselective chromatography. The Arndt−Eistert reaction has witnessed a renaissance in the field of natural products, in particular β‐amino acids and β‐peptides. Ring‐contracting Wolff rearrangements and ketene cycloadditions have been applied in syntheses of increasingly complex, biologically active target molecules. These accomplishments, as well as unsolved problems, are addressed in the present review. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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Section: Laser Flash Photolysis (Lfp)mentioning

confidence: 99%

100 Years of the Wolff Rearrangement

2002

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“…Ketenes are extremely important reactive species, which occur as transients in numerous thermal and photochemical reactions. − In many cases, ketenes have relatively weak UV absorption bands below 400 nm, making them difficult to resolve from other species in UV laser flash photolysis (LFP), although a number of studies of ketene reactivity employing this technique have been reported. − However, all ketenes exhibit a very strong and characteristic IR band in the region of 2100 cm -1 , arising from the out-of-phase or antisymmetric stretch of the CCO moiety . The IR spectroscopy of ketenes has been extensively studied in cryogenic matrices − and has been applied recently to investigate ketene reactions toward nucleophiles in this medium. , We − and others have also recently demonstrated that LFP with time-resolved infrared detection (LFP-TRIR) is ideally suited for both mechanistic and kinetic studies of ketenes in solution since the characteristic spectroscopic region near 2100 cm -1 is transparent to most solvents and void of absorptions due to other photogenerated transients and products. In this paper, we employ LFP-TRIR for systematic studies of the infrared spectroscopic properties of ketenes and explore the mechanism and kinetics of the ketene amine reactions.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopy and Absolute Reactivity of Ketenes in Acetonitrile Studied by Laser Flash Photolysis with Time-Resolved Infrared Detection

et al. 1998

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Laser flash photolysis with time-resolved infrared detection of transients (LFP-TRIR) has been used to study the IR spectroscopy and reactivity of a number of substituted ketenes, prepared by the 308-nm photolysis of α-diazocarbonyl precursors in acetonitrile solution at room temperature. The correlation of the experimental ketene asymmetric stretching frequency to the Swain−Lupton field (F) and resonance (R) effect substituent parameters was unsatisfactory, whereas the correlation to the inductive substituent parameter (σI) of Charton gave excellent results. This suggests that the asymmetric stretching frequency of substituted ketenes depends mainly on the inductive (i.e., field) effect of the substituents. The mechanism and kinetics of the reactions of these ketenes with various amines in acetonitrile were also studied. An intermediate species identified as either zwitterionic ylide or amide enol formed in the nucleophilic addition of the secondary amine to the Cα of the ketene is observed by TRIR. The decay of this species is assisted by the amine and is concomitant with the formation of an amide, the final product of the reaction. Our kinetic data on ketene amine reactions show a general trend, indicating a much higher reactivity (ca. 3 orders of magnitude difference in the corresponding rate constants) of secondary amines compared with that of tertiary amines. Secondary diethylamine shows reactivity similar to those observed for primary amines, while secondary piperidine seems to be, in general, somewhat more reactive. The observed trend is rationalized in terms of the steric effects exerted by both amine and ketene substituents. Our data on para-substituted phenyl ketenes provide support for the negative charge development on the ketene moiety in the transition state, with electron-withdrawing substituents accelerating and electron-releasing substituents slowing down the addition reaction.

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