Aryl derivatives carbopalladation

When the carbopalladation of the bicyclopropylidene is performed in the presence of methyl acrylate, the reaction takes a different course (Scheme 8.34) [79]. The 1,3-diene intermediate 75 reacts in situ with the dienophile to give the spiro[2.5]octane derivative 76. An extension of this cascade Heck-Diels-Alder reaction involving l,3-dicyclopropyl-l,2-propadiene as the alkene partner, an alkenyl or aryl halide and a dienophile has been reported [80]. 

A domino Heck carbopalladation/cyclization reaction of (Z)-3-(2-(but-2-ynyloxy)phenyl)prop-2-en-l-ol 453 with aryl iodides furnishes chroman derivatives 454 in good yield (Equation 185) <2004AGE5997>. 

The palladium-catalyzed reaction of allyl chloride 11 with the benzyne precursor 104 to produces phenanthrene derivatives 131 is also known [83]. A plausible mechanism for this intermolecular benzyne-benzyne-alkene insertion reaction is shown in Scheme 38. Initially n-allyl palladium chloride la is formed from Pd(0) and 11. Benzyne 106, which is generated from the reaction of CsF and 104, inserted into la to afford the aryl palladium intermediate 132. A second benzyne insertion into 132 produce 133 and subsequent carbopalladation to the alkene afford the cyclized intermediate 134. f>- Iydride elimination from 134 followed by isomerization gave 9-methylphenanthrene 131. 

This methodology was used to construct several indole and benzofuran derivatives (00T7541). Oxidative insertion of Pd(0) into the aryl-I bond of 653a,b followed by carbopalladation onto the pendant olefin afforded an intermediate organopalladium... 

An analogous reaction mode is followed in the 1 2 cross-coupling of 2-bromostyrene with acenaphthylene, which yields a bisannelated tetrahydrofulvene (Scheme 48)J Norbomene can favorably serve as a relay for cascade carbopalladations as the /S-hydride elimination is virtually impossible. The reaction always starts with an alkenyl-or arylpaUadium starter, generated either by oxidative addition of an alkenyl or aryl halide to a paUadium(O) species or by hydro- or carbopalladation of an alkyne, adding to the double bond. With /3-bromostyrene, norbomene can yield the same type of bisannelated tetrahydrofulvene derivative " as with acenaphthylene, but under different reaction conditions can also react with a 2 1 stoichiometry to give a cyclohexadiene-annelated norbomane derivative (Scheme 49). ... 

Yet a new mode of reaction was uncovered for endo,exo-bishomobarrelene 260 [380]. Instead of being trapped by hydride to furnish the typical hydroarylation products, the carbopalladation intermediate 261 underwent a rearrangement via 262 and 263 with subsequent -hydride elimination to yield the aryl-substituted monohomobarbaralane derivatives rac-264 (Scheme 8.54) [380]. 

The Heck reactions with subsequent reduction ( hydride-ion capture ) [175, 178, 381] have also become valuable methods for the construction of various carbo- and heterocyclic skeletons. Such a reaction can always occur when the syn addition of an aryl- or alkenylpaUadium species onto a multiple bond leads to an intermediate that does not or cannot undergo a rapid syn- -hydride elimination, such as in the intramolecular carbopalladation of an iodoaryl derivative of type 265 (Scheme 8.55) [178]. 

The complex catalytic cycle commences with oxidative palladium insertion on the aryl iodide bond. The following carbopalladation with norbornene creates a bulky intermediate that is not prone to p-hydride elimination and allows C-H activation of the ortho position of the aryl moiety. Subsequent oxidative addition of the alkyl iodide allows cross-coupling and elimination of the norbornene by retro-carbopalladation. The remaining intermediate 146 then undergoes aMizoroki-Heck reaction with the acrylate, which completes the catalytic process and furnishes the desired cinnamate 148 derivative. 

A reaction sequence involving Heck then Diels-Alder processes and that exploits the propensity of bicyclopropylidene to undergo carbopalladation with aryl- or alkenyl-palladium species has been developed. This ultimately affords spiro[2,5]oct-4-ene derivatives in excellent yield (eq 94). ... 

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