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Bicyclo[6.3.0]undeca‐1(11),2,4,6,8‐pentaen‐10‐ylidene: An Aromatic Carbene with Ambiphilic Properties
Author(s) -
Ishikawa Hiroyuki,
Nishida Junichi,
Jones John W.,
Scott Lawrence T.,
Kawase Takeshi
Publication year - 2017
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201700069
Subject(s) - carbene , chemistry , medicinal chemistry , protonation , electrophile , nucleophile , bicyclic molecule , azulene , photochemistry , organic chemistry , ion , catalysis
The title carbene ( 4 ) was generated as a highly reactive species in solution by photoirradiation of 10‐diazobicyclo[6.3.0]undecapentaene ( 5 ) using a high‐pressure mercury lamp. Carbene 4 reacts with benzene to afford two isomeric adducts, 10‐phenylbicyclo[6.3.0]undecapentaene ( 10 ) and tricyclo[9.3.0 3, 10 .0]heptadeca‐1,3(10),4,6,8,12,14,16‐octaene ( 11 ). The reactivity toward benzene is a characteristic of an electrophilic aromatic carbene analogous to cyclopentadienylidene 1 . In contrast, the reaction of 4 with methanol produces 7‐methoxybicyclo[6.3.0]undeca‐1,3,5,8,10‐pentaene ( 15 ). When [D 1 ]methanol was employed as a reactant, the 10‐deuterated analogue was formed. The results clearly indicate the formation of bicyclo[6.3.0]undecapentaenyl cation ( 7 ) as a novel 10 π‐electronic compound by protonation of 4 . Theoretical calculations indicate that the 2‐ and 7‐positions of the cation have the largest positive charge in the cation. Moreover, the carbene was generated in the presence of tert‐ butyl hydroperoxide in aqueous tetrahydrofuran to afford azulene through oxidation of 7 , followed by decarbonylation. The nucleophilic property of carbene 3 is similar to that of cycloheptatrienylidene 2 . Thus, 4 can be regarded as a novel ambiphilic aromatic carbene.