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The Catellani reaction was discovered by Professor Marta Catellani (Università degli Studi di Parma, Italy) and co-workers in 1997. The reaction uses aryl iodides to perform bi- or tri-functionalization, including C-H functionalization of the unsubstituted ortho position(s), followed a terminating cross-coupling reaction at the ipso position. This cross-coupling cascade reaction depends on the ortho-directing transient mediator, norbornene.



Reaction mechanism
The Catellani reaction is catalyzed by palladium and norbornene, although in most cases superstochiometric amounts of norbornene to deduce reaction time. Palladium(0) oxidatively inserts in to aryl-iodide bond. The Pd(II) species coordinates with the double-bond of the norbornene and undergoes electrophilic cyclopalladates at the ortho position. The structure of the norbornylpalladium intermediate does not allow for ß-hydride elimination in either of the the ß-positions due to Bredt's Rule over bridgehead proton and the trans-configuration of the palladium and proton. The second oxidative addition occurs with the corresponding coupling partner to form a Pd(IV) intermediate, which then reductively eliminates and completes the first cross-coupling bond formation. After the elimination of norbornene, the Pd(II) species undergoes the second cross-coupling reaction, terminating the series with a number of traditional palladium-catalyzed coupling reactions.

OMIT: Rhodium can also be used as a catalyst along with norbornene instead of palladium.



Steps of the Catellani reaction:
 * 1) Oxidative addition
 * 2) Carbopalladation of norbornene
 * 3) Palladacycle formation
 * 4) Oxidative addition to palladacycle
 * 5) Reductive elimination from palladacycle
 * 6) Norbornene extrusion
 * 7) Termination via Heck reaction, Suzuki reaction, etc.

Ortho and ipso cross-coupling partners
The Catellani reaction facilitates a variety of C—C and C—N bond-forming reactions at the ortho position. These include alkylation from alkyl halides, arylation from aryl bromides, amination from benzyloxyamines,   acylation from anhydrides. Likewise in the case of terminating ipso coupling partners with Heck-type termination with olefins, Suzuki-type reaction with boronic esters, borylation with bis(pinacolato)diboron, protonation with i-PrOH, decarboxylative alkynylation with alkynyl carboxylic acids.

Uses
With tethered cross-coupling partners, Lautens, Malacria, and Catellani used this reaction to construct a variety of fused ring systems since 2000.

The Catellani reaction has been used as a key step for the total synthesis (+)-linoxepin, rhazinal, aspidospermidine, and (±)-goniomitine.