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Valence bond isomers heterocycles

Relatively few examples of photoreactions of seven-membered and larger heterocycles have been reported. The major products of irradiation of liquid oxepin are hex-5-en-l-ol and hexanal234 photodecomposition of cyclic ethers has, in general been shown to be largely dependent on ring size. Irradiation of the valence bond isomer (287) of hexakis(trifluoromethyl) oxepin gave the unexpectedly stable oxet (288) via a mixture of (Z)- and... [Pg.50]

Since the late 1960s photoreactions of heterocyclic compounds have been investigated extensively. Valence-bond isomers have been proposed as intermediates, but their isolations have succeeded only in the last 10 years. In this review, we shall consider the valence-bond isomers of heterocyclic compounds having four-membered rings Dewar heterocycles. [Pg.170]

Irradiation of tetrakis(trifluoromethyl)thiophene gave a valence-bond isomer which Heicklen first proposed to have a Dewar structure,9 then a cyclopropenyl thioketone,10 and still later11 a Dewar form. The structure was shown to be Dewar form 1 by 19F and 13C NMR and by the study of its reactions (Eq. 8).12 14 This is the first isolated example of a Dewar viner of a five-membered heterocycle. [Pg.173]

After a brief survey of the history of valence-bond isomers of aromatic compounds, new syntheses and the reactions of these isomers reported in the last decade are reviewed. In the second chapter, the valence-bond isomers of homoaromatic compounds, especially benzene derivatives, are described and in the third chapter those of heterocyclic compounds. Photoreactions of perfluoroalkylated aromatic compounds afford valence-bond isomers in high yields. These isomers are very stable and useful for the synthesis of highly strained compounds. Therefore, the emphasis is put on the chemistry of trifluoromethylated benzvalenes, Dewar thiophenes, and Dewar pyrroles. [Pg.103]

In this review the progress of the chemistry of valence-bond isomers during and after the 1970 s is discussed. For convenience, the chemistry of homoaromatic compounds is treated first followed by a discussion of heterocyclic compounds. [Pg.104]

Since a review on Dewar heterocyclic compounds has been published recently102), in this chapter only some typical reactions of valence-bond isomers of heteroaromatic compounds will be discussed. The emphasis will be placed on the chemistry of trifluoromethylated Dewar thiophene and pyrroles, both of which are rare examples of stable valence-bond isomers of heterocyclic compounds. Since the isolation of valence-bond isomers of heteroaromatic compounds is mostly limited to the per-fluoroalkylated isomers, those postulated as intermediates are also included. [Pg.128]

There are many kinds of six-membered heterocyclic compounds but only few valence-bond isomers have been isolated. Thus, we will first describe the photoreactions of pyrones and pyridones and subsequently those of the usual heteroaromatic compounds with increasing number of hetero atom s. [Pg.136]

Seven-membered heterocyclic compounds such as oxepin or azepin are not considered to be aromatic, and the number of their valence bond isomers is so large that we cannot describe all these compounds. Therefore, only a few interesting examples will be given. [Pg.145]

The thermal back reaction to the tricyclic compound has attracted our attention. The application of this reaction to a cyclopropenyl ketone imine system gives a similar isomer of a diazepin compound (165)181). This is the first synthesis of a valence-bond isomer of a nitrogen-containing heterocyclic compound having a bicyclobutane part. [Pg.146]

Barlow, M.G., Dingwall, J.G., and Haszeldine, R.N., Valence-bond isomers of heterocyclic compounds isomers of pentakis-(pentafluoroethyl)pyridine, /. Chem. Soc., Chem. Commun., 1580, 1970. [Pg.2018]


See other pages where Valence bond isomers heterocycles is mentioned: [Pg.226]    [Pg.60]    [Pg.226]    [Pg.250]    [Pg.250]    [Pg.110]    [Pg.32]    [Pg.32]    [Pg.302]    [Pg.72]    [Pg.32]    [Pg.23]    [Pg.349]    [Pg.421]    [Pg.37]   
See also in sourсe #XX -- [ Pg.319 ]




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