Aromatization carbene-olefin addition

It might be expected that the aromatic character of (14) would lend unique characteristics to its chemistry. Studies of the olefin addition and C—H insertion reactions of the carbene, however, indicate that it is poorly stabilized and highly reactive.<26)... 

Additions include the attachment of two univalent atoms or groups (called addends) to an unsaturated system, e. g., to olefins, carbonyl groups, aromatic systems, carbenes, etc. (Rule 2.1). For example, the addition of hydrocyanic acid to the car-... 

What about a nucleophilic carbene, for which negative charge should build up on the olefinic carbon atoms during the carbene addition cf. 5 With ArCH=CH2 substrates, electron-withdrawing aryl substituents would stabilize such a transition state and the p value should be positive. There are several examples of this phenomenon. For example, cycloheptatrienylidene, 10, adds to / -substituted styrenes with p = -t-1.02 - 1.05 (vs. a) consistent with a nucleophilic selectivity that seems to implicate the aromatic resonance form 10a as an important feature of the carbene. [45] It is satisfying to compare this result with p = -0.76 (vs. a) or -0.46 (vs. a" ") for additions to styrenes of cyclopentadienylidene, 11, where contributions of the cyclopentadienide form (11a) would render the carbene electrophilic. [46] However, these conclusions are too facile. There is reason to believe that the chemistry attributed to 10 might in fact be due to its allenic isomer 12. [47] And the electronic structure of 11 is also more complicated than the simple depiction above. [48]... 

Dinuclear rhodium complex with 36 was active in the addition reactions of carbenes (Scheme 4.22). Moreover, Ihe yield decreased for the stericaUy hindered olefins compared with rhodium acetate (II) due to steric factors. Furthermore, this complex preferably catalyzed the inclusion of carbene to the CH bond of aromatic fragment [82],... 

Other reactions of sulphonium ylides include o /9 -elimination,metal-mediated carbene-transfer to olefins, insertion into aromatic C—H bonds or other carbenoid-type processes, formation of Pd" complexes, addition to enones (forming cyclopropyl ketones or heterocycles ), reaction with isoquinoline 2-oxide, and [2,3]-sigmatropic rearrangements " [as in the case of (12) 1 or... 

Carbenes, addition to multiple bonds, 61 addition to olefins, 59, 60 analogy with carbonium ions, 60 co-ordination reactions of, 61 dibromo-, see dihalocarbenes dichloro-, see dihalocarbenes dihalo-, addition to olefins, 59, 61 dihalo-, deoxygenation of aromatic N-oxides by, 77... 

The first example of olefinic C-H addition to iV-sulfonylaldimines and aryl aldehydes has been achieved through olefinic C-H bond activation by a rhodium complex. C-H bond functionalization by Rh(III) catalysts has also been used to achieve arylation of N-protected aryl aldimines by 2-arylpyridine and benzamide mechanistic studies have provided insight for further development of this means of creating a-branched amine functionality. A cobalt-A-heterocyclic carbene (NHC) catalyst has also directed arylation of aromatic aldimines through C-H bond functionalization of 2-arylpyridines. ... 

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