Arenes carbopalladation

Recently, synthesis of aryl ketones by a combination of palladium-catalyzed C-H activation of arenes and intermolecular carbopalladation of nitriles has been reported (Equation (119)).474... 

Termination of cascade carbopalladation sequences by arylation can play a major role in systems that form a reasonably long-lived palladium intermediate and contain a suitably functionalized arene moiety in the vicinity of the organopalladium function. In particular, neopentylpalladium intermediates have been found to intramolecularly attack an adjacent arene moiety. For example, iodoarenes 149 with electron-withdrawing substituents in the... 

Scheme 38 Inter-intramolecular carbopalladations involving formal C-H bond activation of an arene moiety7 ...

The final option available to a u-alkylpalladium intermediate from Heck alkylation occurs if another alkene or alkyne function is situated properly to participate in a further Heck-type carbopalladation (equation 161)318,319. In properly constructed systems, more than one further carbopalladation is feasible, and many examples of these cascade car-bopalladations have been reported. Several have been quite spectacular (equation 162)320. Fused, spirocyclic and bridged bicyclic ring systems have been prepared in this manner. The process may also create as many as five rings in one step, with five-,six- and three-membered rings321 being the most suitable for preparation (equation 163). Alternatively, the proper orientation of double and triple bonds allows cyclotrimerization to highly functionalized arenes or fulvenes (equation 164)322,279. 

Brase S, de Meijere A (2002) Palladium-Catalyzed Cascade Carbopalladation Termination with Alkenes, Arenes, and Related jr-Bond Systems. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1369... 

IV.3.1 Palladium-Catalyzed Cascade Carbopalladation Termination with Alkenes, Arenes, and Related ir-Bond Systems... 

The carbopalladation of a triple bond is faster than that of a double bond, even when the alkene is tethered to the initially formed arylpalladium halides. This is exemplified by the formation of a tetracyclic system from o-isobutenyliodobenzene and diphenylethyne. This process is also terminated by ortho attack of the intermediate neopentyl-type alkyl-palladium halide on one of the arene rings (Scheme... 

As in the cases of termination by lactonization and lactamization, some specially structured alkenes, such as norbomene and related alkenes, can participate in intermolecular carbopalladation-carbonylative ketonization tandem processes. In the reactions shown in Scheme 22, the acylpalladium intermediates undergo intramolecular acylpalladation with arenes to provide ketones. ... 

IV.6.2 Arene Substitution Involving Temporary Incorporation and Removal of Carbon Tethers via Carbopalladation and Decarbopalladation... 

Carbopalladation is the reaction of a cr-bonded organopalladium complex I with an unsaturated molecule (such as an alkene 2) to yield the migratory insertion product 3 (Scheme 1). The reaction is tremendously flexible, allowing for a wide variety of structural types for both reactants 1 and 2. The precursors of palladium complexes 1 are commonly alkenyl or aryl halides or triflates (8 and 9, respectively), the reaction of which is more commonly termed the Heck reaction. Allylic systems 10, which react to provide -Tr-allylpalladium complexes, can participate in the reaction as can benzylic precursors 11. Acylpalladium complexes 12 also react and are commonly generated in the same reaction vessel by Pd-catalyzed carbonylation. Their unsaturated reaction partners include alkenes 2, alkynes 4, dienes 6, allenes, and arenes, all of which can be electron rich or poor. Carbopalladation occurs in a syn fashion allowing the installation of stereocenters (2- 3) or control of alkene geometry (4- 5). 

Erase, S. and de Meijere, A. (2002) Palladium-catalyzed tandem and cascade carbopalladation -termination with alkenes, arenes and related jr-compounds, mHandbook of Organo-Palladium Chemistry (ed. E.-i. Negishi), John WUey Sons Inc., New York, pp. 1369 05. 

Polycyclic Arenes. Trimethylsilylphenyl triflates have found widespread use as benzyne precursors in the preparation of polycyclic arenes. Triphenylenes are made via paUadium-catalyzed [2 + 2 + 2] cyclotrimerization of arynes, by paUadium-catalyzed annulation of the aryne and 2-halobiaryls, or via carbopalladation/carbocycUzation of arynes with substituted iodobenzenes (eq 2). All three approaches furnish substituted triphenylenes in high reported yields. Substituted phenanthrenes or naphthalenes are similarly prepared using 2-(trimethylsilyl) phenyl triflate as an aryne precursor. Treatment of the reagent with fluoride, a palladium catalyst, and a deactivated alkene, allyl halide, or internal aIk5Tie provides 9-substituted or 9,... 

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