<b>Bicyclo [2.2.0]hexa-2,5-diene</b>

Tamelen, E. E. Van; Pappas, S. Peter

doi:10.1021/ja00903a056

Cited by 170 publications

(45 citation statements)

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“…[3] Syntheses of the first Dewar benzenes were performed in the 1960s by a clever choice of conventional reactions and/or UV irradiation of suitable precursors; they became the first isolated valence-bond isomers of benzene. [4] Facile isomerization of DBs into their more stable isomers Ϫ benzenes Ϫ can be achieved cleanly and quantitatively under thermal or photochemical conditions. Soon after these reports, a remarkable trimerization reaction of 2-butyne in the presence of AlCl 3 for the preparation of hexamethyl[2.2.0]bicyclohexa-2,5-diene (hexamethyl-DB) in reasonable yields was discovered.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Rearrangement of Dewar Benzenes Into Biaryls: Experimental Evidence for Conrotatory Ring Opening

et al. 2007

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Rearrangement of aryl‐substituted Dewar benzenes into the corresponding biaryls may serve as an alternative pathway for synthesis of sterically hindered biaryls. The kinetic data obtained from thermal rearrangements of Dewar benzenes provide experimental evidence for the proposed orbital‐symmetry‐controlled electrocyclic ring opening. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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Section: Introductionmentioning

confidence: 99%

Synthesis and Rearrangement of Dewar Benzenes Into Biaryls: Experimental Evidence for Conrotatory Ring Opening

et al. 2007

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“…[1,2] Chemists have long been fascinated by finding exceptions from these rules.S tarting in the 1960s,v alence isomers of benzene were prepared through elaborate organic syntheses, [3][4][5][6] while hypercoordinated carbon compounds entered the stage through the pioneering work of Olah on superacids and non-classical cations. [7,8] Theb onding situation in protonated methane (CH 5 + ), which is the most prominent representative of pentacoordinated carbon, is best described as a3-center 2-electron bond between H 2 and CH 3 + ,but its isolation in bulk is elusive.The replacement of hydrogen with organogold species lead to the isolation of penta-and hexacoordinated methanium salts by Schmidbaur.T hese carbido clusters,[ (Ph 3 PAu) 5 …”

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confidence: 99%

Crystal Structure Determination of the Pentagonal‐Pyramidal Hexamethylbenzene Dication C₆(CH₃)₆²⁺

Malischewski

Seppelt

2016

Angew Chem Int Ed

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In contrast to the well-known 2-norbornyl cation, the structure of which was am atter of long debate until its pentacoordinated nature was recently proven by an X-ray structure,t he pentagonal-pyramidal dication of hexamethylbenzeneh as received considerably less attention. This species was first prepared by Hogeveen in 1973 at low temperatures in magic acid (HSO 3 F/SbF 5 ), for whichh ep roposed an onclassical structure (containing ah exacoordinated carbon) based on NMR spectroscopya nd reactivity studies,b ut no Xray crystal structure has been reported. C 6 (CH 3 ) 6 2+ can be obtained through the dissolution of hexamethyl Dewar benzeneepoxideinHSO 3 F/SbF 5 and crystallized as the SbF 6À salt upon addition of excess anhydrous hydrogen fluoride.T he crystal structure of C 6 (CH 3 ) 6 2+ (SbF 6 À ) 2 ·HSO 3 Fc onfirms the pentagonal pyramidal structure of the dication. The apical carbon is bound to one methyl group (distance 1.479(3) )and to the five basal carbon atoms (distances 1.694(2)-1.715(3) ).The tetravalencyo fc arbon and the hexagonal-planar ring structure of benzene are fundamental axioms of organic chemistry,a nd were developed 150 years ago by KekulØ. [1,2] Chemists have long been fascinated by finding exceptions from these rules.S tarting in the 1960s,v alence isomers of benzene were prepared through elaborate organic syntheses, [3][4][5][6] while hypercoordinated carbon compounds entered the stage through the pioneering work of Olah on superacids and non-classical cations. [7,8] Theb onding situation in protonated methane (CH 5 + ), which is the most prominent representative of pentacoordinated carbon, is best described as a3-center 2-electron bond between H 2 and CH 3 + ,but its isolation in bulk is elusive.The replacement of hydrogen with organogold species lead to the isolation of penta-and hexacoordinated methanium salts by Schmidbaur.T hese carbido clusters,[ (Ph 3 PAu) 5 C]+ and [(Ph 3 PAu) 6 C] 2+ ,a re significantly stabilized by aurophilic interactions. [9,10] Recently,arelated structural motive has been identified in the iron-molybdenum nitrogenase cofactor, which contains hexacoordinated C 4À .[11] Taking ac ompletely different approach, Akiba and co-workers prepared formally hypercoordinated organic species through special ligand design, where an electrophilic carbon atom is intramolecularly coordinated by two/four neighboring methoxy groups. TheC À Odistances are in the range of 2.43(1)-2.45(1) and 2.641(5)-2.750(5) ,r espectively, [12,13] thus indicating only weak interactions.Instark contrast, hypercoordinated carbon with much shorter bonds can be found in carboranes. Nevertheless,t hese common structural motives of boron chemistry are only subtly changed by replacing boron with an isolobal carbon fragment. Surprisingly,e ven hexagonalplanar carbon has been considered viable (based on theoretical calculations by Exner and Schleyer) in boron compounds, for example,inC B 6 2À . [14] Recently,t he isolation of the non-classical norbornyl cation and its crystal structure ana...

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“…The first six are topologically possible valence isomers of (CH) 6 . [17][18][19][20][21][22] Two non-planar and one planar six-membered rings are theoretically found ones in P 6 23) and in anionic silicon clusters, 8) respectively. Ab initio molecular orbital and density functional theory (DFT) calculations were performed using the Gaussian03 software package.…”

Section: Theoretical Methodsmentioning

confidence: 99%

Theoretical Investigation of Stable Structures of Ge<SUB>6</SUB> Clusters with Various Negative Charges

Kikuchi

Takahashi

2006

Mater. Trans.

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Bicyclo [2.2.0]hexa-2,5-diene

Cited by 170 publications

References 5 publications

Synthesis and Rearrangement of Dewar Benzenes Into Biaryls: Experimental Evidence for Conrotatory Ring Opening

Synthesis and Rearrangement of Dewar Benzenes Into Biaryls: Experimental Evidence for Conrotatory Ring Opening

Crystal Structure Determination of the Pentagonal‐Pyramidal Hexamethylbenzene Dication C₆(CH₃)₆²⁺

Theoretical Investigation of Stable Structures of Ge<SUB>6</SUB> Clusters with Various Negative Charges

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Bicyclo [2.2.0]hexa-2,5-diene

Cited by 170 publications

References 5 publications

Synthesis and Rearrangement of Dewar Benzenes Into Biaryls: Experimental Evidence for Conrotatory Ring Opening

Synthesis and Rearrangement of Dewar Benzenes Into Biaryls: Experimental Evidence for Conrotatory Ring Opening

Crystal Structure Determination of the Pentagonal‐Pyramidal Hexamethylbenzene Dication C6(CH3)62+

Theoretical Investigation of Stable Structures of Ge<SUB>6</SUB> Clusters with Various Negative Charges

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Crystal Structure Determination of the Pentagonal‐Pyramidal Hexamethylbenzene Dication C₆(CH₃)₆²⁺