Cumulenes cyclic

Treatment of geminal dihalocyclopropyl compounds with a strong base such as butyl lithium has been for several years the most versatile method for cumulenes. The dihalo compounds are easily obtained by addition of dihalocarbenes to double--bond systems If the dihalocyclopropanes are reacted at low temperatures with alkyllithium, a cyclopropane carbenoid is formed, which in general decomposes above -40 to -50°C to afford the cumulene. Although at present a number of alternative methods are available , the above-mentioned synthesis is the only suitable one for cyclic cumulenes [e.g. 1,2-cyclononadiene and 1,2,3-cyclodecatriene] and substituted non-cyclic cumulenes [e.g. (CH3)2C=C=C=C(CH3)2]. 

Strained Cyclic Alkynes, and Strained Cyclic Cumulenes. 

A derivative of cyclopentyne has been trapped in a matrix. Although cycloheptyne and cyclohexyne have not been isolated at room temperatures, Pt(0) complexes of these compounds have been prepared and are stable." The smallest cyclic allene" so far isolated is l-/err-butyl-l,2-cyclooctadiene 107." The parent 1,2-cyclooctadiene has not been isolated. It has been shown to exist transiently, but rapidly dimerizes." " The presence of the rert-butyl group apparently prevents this. The transient existence of 1,2-cycloheptadiene has also been shown," and both 1,2-cyclooctadiene and 1,2-cycloheptadiene have been isolated in platinum complexes." 1,2-Cyclohexadiene has been trapped at low temperatures, and its structure has been proved by spectral smdies." Cyclic allenes in general are less strained than their acetylenic isomers." The cyclic cumulene 1,2,3-cyclononatriene has also been synthesized and is reasonably stable in solution at room temperature in the absence of air." ... 

Studies on Cg show that cyclic cumulenes are not well described by a one-determinant wavefunction. In a valence-CASSCF calculation on cyclic Cg, for example, the Hartree-Fock determinant has a weight of only 0.40. The problem is assumed to be aggravated for larger systems, as the HOMO-LUMO gap diminishes. 

The A state of 4b is predicted to be a transition state for interconversion of the enantiomers of a cyclic cumulene (7 in Fig. 12) that is an isomer of 3b. In 7 the roles of the lone pairs on nitrogen and carbon are reversed, so that the nitrogen is the central atom of a 2-aza-allene unit, formed by overlap of the... 

Arynes, Strained Cyclic Alkynes, and Strained Cyclic Cumulenes. .. 42 147... 

Cyclic allenes in general are less strained than their acetylenic isomers.345 The cyclic cumulene 1,2,3-cyclononatriene has also been synthesized and is reasonably stable in solution at room temperature in the absence of air,34 ... 

Silirenes (140, equation 32) could also be involved in the transition-metal catalyzed decomposition of bis(diazoketones) 139 which provides the electron-rich [4]radialenes 14266,67. While the formation of 142 directly from silirene 140 cannot be excluded a priori, it is more reasonable to assume that 140 undergoes twofold ring-expansion to form the cyclic cumulene 141, which then provides 142 by a cyclodimerization reaction. The intermediacy of 141 is corroborated by the isolation of the Diels-Alder product 14366. 

Two reactions which involve addition of sulfur reagents to alkenes have been reported for the first time. In the first, a mercapto[15]annulenone can be prepared from an annu-lenone by heating with sodium sulfide and elemental sulfur313 (equation 50). In the second, addition of sulfur to cyclic cumulenes gave rise to a series of interesting cyclizations, the... 

Strain in cyclic cumulenes is similarly relieved by complexing one of the double bonds to a transition metal. Most of the research in this area has appeared since the late 1980s, and to date no review has appeared. The second purpose of this article is to fill this void. 

A polycyclic system with a l,3-dioxa-2-silacyclohepta-4,6-diene fragment was obtained in low yield from bis(diazocarbonyl)silane 671. In the first stage, a biscarbene or a biscarbenoid, generated in the presence of copper triflate or palladium acetate, forms 1,2-diacylcyclopropene, then rearranging into cyclic cumulene triene 672 by migration of a silicon atom to an oxygen atom. The latter dimerizes to [4]-radialen 673 or reacts with furan to afford 674 (Scheme 32) (89AG175()). 

A I Edited by Randolph P. Thummel, Department of Chemistry, University of Houston Volume 1,1989,467 pp. 97.50 ISBN 0-89232-869-X CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Randolph P. Thummel. Isobenzo-furans, Bruce Rickbom. Dihydropyrenes Bridged [14] Annu-lenes Par Excellence. A Comparison with Other Bridged Annulenes, Richard H. Mitchell. [I.m.n.] Hericenes and Related Exocyclic Polyenes, Pierre Vogel. The Chemistry of Penta-cyclo [SAO.O. O3,1 °.05,9] Undecane (PCUD) and Related Systems, Alan P. Marchand. Cyclic Cumulenes, Richard P. Johnson. Author Index. Subject Index. 

Zahradnik, R. Hobza, P. Burd, R. Hess, B.A. Radziszewski, J. Strained unsaturated molecules. Theoretical study of acyclic and cyclic cumulenes and acetylenes. J. Mol. Struct. 1994, 313, 335-349. 

Moore and Ozreticif synthesized A, 2 ,-cyclodecatriene (3), a cyclic cumulene, by treating A1,2-cyclononadiene (1) with one equivalent of phenyl (tribromomethyl)-mercury in refluxing benzene, followed by removal of phenylmercuric bromide and the solvent, and obtained 10,10-dibromobicyclo[7.1.0]decene-l,2 (2), which on reaction with inethyllithium afforded the cumulene (3). 

Bennett MA, Schwemlein HP (1989) Angew Chem Int Ed Engl 28 1296 Buchwald SL, Broene RD (1995) In Abel EW, Stone EGA, Wilkinson G (eds) Hegedus LH (vol ed) Comprehensive organometallic chemistry 11, vol 12. Pergamon, Oxford, p 771 Jones WM,Klosin J (1998) Transition metal complexes of arynes, strained cyclic alkynes, and strained cyclic cumulenes. In Stone EGA, West R (eds) Adv Organomet Chem, vol 42. Academic, San Diego, p 147... 

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