Cyclopropenones chemistry

The origin of cyclopropenone chemistry goes back to the successful preparation of stable derivatives of the cyclopropenium cation <5 3), the first member of a series of Huckel-aromatic monocyclic carbo-cations possessing a delocalized system of (4n + 2)-7r-electrons. This experimental confirmation of LCAO-MO theory stimulated efforts to prepare other species formally related to cyclopropenium cation by a simple resonance description of electron distribution, namely cyclopropenone 7 and methylene cyclopropene (triafulvene) 8 ... 

Library of Congress Cataloging in Publication Data. Main entry under title Cyclic compounds. (Topics in current chemistry 57). Bibliography p. Includes index. CONTENTS Eicher, T. and Weber, J. L. Structure and reactivity of cyclopropenones and triafulvenes. — Sargent, M. V. and Cresp, T. M. The higher annulenones. 1. Cyclic compounds—Addresses, essays, lectures. I. Eicher, Theophil, 1932- II. Series. 

The lack of additional thermochemical data is admittedly frustrating because there are many other documented cyclopropenones [e.g., see W. E. Billups and A. W. Moorehead, in The Chemistry of the Cyclopropyl Group (Ed. Z. Rappoport), Chap. 24, Wiley, Chichester, 1987, p. 1533] which have higher stability and alternative amounts of conjugation with the affixed substituents. 

S CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Dennis P. Curran. Intramolecular 1,3-Dipolar Cycloaddition Chemistry, Albert Padwa and Allen M. Schoffstall. Stereochemical and Synthetic Studies of the Intramolecular Diels-Alder Reaction, William R. Roush. Thermal Reaction of Cyclopropenone Ketals, Key Mechanistic Features, Scope and Application of the Cycloaddition Reactions of Cyclopropenone Ketals and p - Delocalized Singlet Vinyl Carbenes Three Carbon 1,1-/1,3-Dipoles, Dale L. Boger and Christine E. Brotherton-Pleiss. Index. 

In a recent study of the chemistry of Ae cyclopropenone acetal (60), the very interesting transformation shown in equation (3) was achieved. Although this conversion was the only reported example of this novel process, it seems likely that the use of other functionalized and (or) stereochemically modfied reagents would provide efficient syntheses of a wide variety of interestingly substituted seven-membered rings. 

The chemistry of the resonance-stabilized cyclopropenone (56) and its derivatives has been the subject of three reviews each of which has encompassed the synthetic procedures employed. The parent unsubstituted molecule (56) is readily available from 2,3-dichloropropene via 1,1-dimethoxycyclopropene (cf. equation 24) and is stable for long periods when stored under inert gas at temperatures below its melting point of — 29° C. Although the acid-catalysed hydrolysis of the acetal as the final step of the sequence proceeds in 90 % yield, the overall yield from the dichloropropene is about... 

Cyclopropenethiones are readily available (Section II.F) and in many respects their chemistry is similar to that of the enones. Whilst X-ray results from diphenylcycloprop-enethione (362) imply little contribution of the dipolar form, MO calculations strongly support the aromatic charge-separated system with a n electron density on sulphur higher than on the oxygen in cyclopropenone. The infrared and Raman spectra of 362 and its perdeuterio derivative have been obtained and the bands assigned by normal coordinate analysis. When compared to the spectrum of diphenylcyclopropenone (14) shifts to 1786 and 1352cm are found °°. 

Due to its ready availability, the chemistry of diphenylcyclopropenone has been investigated more extensively than any of the other cyclopropenones. Nevertheless, the chemistry of a sizeable number of these compounds has now been reported ... 

Cyclopropenone itself seems to exhibit its own unique chemistry. The compound can be kept at its melting point ( — 28° Q for several weeks but polymerizes rapidly at room temperature. It is stable in organic solvents at room temperature. In aqueous solution no hydration can be detected by infrared spectroscopy. 

For further examples of cyclopropenone transition metal chemistry see Section 5.C. 

C. Cyclopropenones and Heteroanalogs Coordination Chemistry Houben-Weyl... 

A-2-Unsaturated three-membered systems are unknown as stable molecules because they would have a four-electron 7t-system, and thus be antiaromatic. 1//-Azirines occur as reactive intermediates and there is evidence for the existence of 2-thiirene in a low-temperature matrix. Azirines, by contrast, are well-known stable compounds. Thiirene A.A-dioxides are also stable molecules, probably best likened to cyclopropenones. The chemistry of saturated three-membered heterocycles is, however, very extensive - epoxides (oxiranes), and to a lesser extent, aziridines are important intermediates in general synthesis. 

A related reaction type is the high pressure (6.2 kbar) Diels-Alder reaction of 2-pyrones with cyclopropenone ketals 16 to give isolable bicycloadducts 17, which then undergo cycloreversion, electrocyclic rearrangement, and ketal hydrolysis leading to tropones. Tropolones also have been formed in this way. This tropolone annulation chemistry was the partial subject of a review in 1990, and it was exploited in the syntheses of some naturally occurring tropoloisoquinolines 18-20. ... 

The authors who have made the largest contribution to our knowledge of the chemistry of cyclopropenone commented that it is apparent that the chemistry of cyclopropenone cannot be extrapolated either from reactions of substituted cyclopropenones or from simple ideas based on the usual reactions of alkene or carbonyl groups [109]. It thus seems apposite to consider the chemistry of cyclopropenone itself severally substituted cyclopropenones are dealt with in the succeeding section. 

POL 03] POLOUKHTINE A., PopiK V.V., Highly Efficient Photochemical Generation of a Triple Bond Synthesis, Properties, and Photodecaibonylation of Cyclopropenones , Journal of Organic Chemistry, vol. 68, pp. 7833-7840, 2003. 

Poloukhtine, A. and Popik, V.V. (2003) Highly efficient photochemical generation of a triple bond synthesis, properties, and photodecarbonylation of cyclopropenones. Journal of Organic Chemistry, 68(20), 7833-7840. 

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