Carbopalladation trapping

E. TANDEM AND CASCADE PROCESSES INVOLVING CYCLIC CARBOPALLADATION-TRAPPING WITH ENOLATES... 

A clean twofold Heck coupling of unsubstituted butadiene 46 (R = H) in the 1- and 4-positions has not been reported. However, the initial carbopalladation product from 46 (R = H) and an in situ formed arylpalladium halide, the cr-allylpalladium halide 47 equilibrating with the corresponding 7r-allylpalladium halide, can efficiently be trapped with the anion formed by arylation of malononitrile or cyanoacetate to give 48, a product of reductive 1,4-arylation-alkylation of 1,3-butadiene 46 (R = H)." /3-Hydride elimination from the intermediate 47 (R H) can be accomplished when the reaction is carried out in the presence of silver acetate or thallium acetate, leading to the... 

Grigg and Xu have developed a variety of so-called queuing cascades involving allenes. The intra-intermolecular carbopalladation sequence of the <9-iodo-A-methyl-A -(methylallyl)aniline 142 and 1,1-dimethylallene 143 with subsequent / -dehydropalladation leads to the 1,3-dienyl-substituted indole derivative 144, which is immediately trapped by an added dienophile (e.g., A-methylmaleimide) in a Diels-Alder reaction to yield 145 (Scheme 37)7 ... 

The aminopalladation and subsequent carbonylation proceed smoothly. The aminopalladation of one of the double bonds of allene 129 generates 130, and CO insertion affords the ester 131 [96]. The carbopalladation of the optically active N-vinyl carbamate 132 with malonate afforded 133. Then CO insertion and trapping with vinylstannane produced the ketone 134 with 95% de, which was converted to 135 [97]. 

Nucleophilic trapping agents used in the Type II Ac-Pd process are not limited to MeOH and other alcohols. A wide range of heteroatom and carbon nucleophiles may be used as in the cases of the Type II cyclic carbopalladation processes terminated by various nucleophilic reagents (Sect. 2.1.2). A couple of reactions shown in Scheme 58 [ 145] provide additional examples of heterocycles synthesis via Type II Ac-Pd process terminated by cross-coupling. 

Cacchi S, Fabrizi G (2002) Carbopalladation of Alkynes Followed by Trapping with Nucleophilic Reagents. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1335... 

The utility of bicyclopropylidene (37) in multicomponent reactions is greatly enhanced by the fact that in the presence of tris(2-furyl)phosphine (TFP) instead of triphenylphosphine, the carbopalladation with an arylpal-ladium halide does not lead to an alkylidenecyclopropane of type 41, but to a CT-allyl-/7r-allylpalladium complex 53/54 which can quite efficiently be trapped with various nucleophiles (Scheme 8). The formal rearrangement... 

Based upon the studies on the mechanism of the Cl sequence we rationalized that the elusive allenol intermediate 19 (Chap. 2.2) could participate in intramolecular trapping reactions as an allenyl ether. Furthermore, vinyl allenes are perfectly suited as dienes in Diels-Alder reactions. Considering both reactive functionalities, allenyl ethers and vinyl allenes, which are perfectly suited for domino processes, we designed an insertion sequence based upon cyclizing carbopalladation [76], where the vinyl aUene results from an isomerization of an alkynylation of a vinyl... 

Although no cyclic carbopalladation is involved, the synthetic potential of the tandem process shown in Scheme 32 [106] consisting of conjugated diene carbopalladation and trapping of the resulted jr-allylpalladium derivatives with enolates appears to be very high. 

Negishi and co-workers demonstrated the feasibility of this carbopalladation mode on an allene in an intramolecular approach to medium and large rings [80]. The new C —C bond is fornied at the central carbon atom of the allene moiety to give a jr-allylpalladium complex, which in turn can be trapped by a variety of nucleophiles (arylstannanes to give arylated products, malonates, phenols, amines, etc.) (Scheme 3-27). The yields are remarkably good without using sophisticated nucleophile delivery techniques. 

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