Carbopalladation nucleophilic trapping

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. 

Both reaction modes A and B have been observed for carbopalladations of methylenecyclopropane derivatives 59a,b with subsequent intramolecular nucleophilic trapping of the intermediate allylpallatium species in or IV, respectively, depending on the tether lengths between the methylenecyclopropane and the dimethyl malonate moieties. The same carbopalladations of unsubstituted methylenecyclopropane 43 (=60a) and pentyli-dene-cyclopropane (60b) with subsequent intermolecular trapping by carbon nucleophiles were found to generally proceed by mode B via intermediates II, V, IV to yield ringopening products 61 and 62, respectively (Scheme 16). 

C. INTERMOLECULAR CARBOPALLADATION OF ALLENES FOLLOWED BY INTERMOLECULAR NUCLEOPHILIC TRAPPING... 

In these cases the interactions between and play the major role to determine the stereochemical outcome of the sequence of an intermolecular carbopalladation and an in-termolecular nucleophilic trapping. Some typical results are listed in Scheme 12. In the case of 29, the methyl group at the 2-position of the alkenyl bromide clearly shifts the equilibrium between anti-26 and syn-16 exclusively to anti-26 (Scheme 2)P ... 

As outlined in Sect. B and C, catalytic intermolecular carbopalladations of allenes followed by either /3-hydride elimination or intermolecular nucleophilic trapping provide 1,3-dienes or allyl derivatives bearing the nucleophile moiety, respectively, while an intermolecular carbopalladation followed by intramolecular trapping sequential reaction provides cyclic skeletons (Scheme 27). In Type I, the nucleophilic moiety is connected with the C—X bond, and in lype II it is attached to the allene moiety. 

Scheme 8.32 Intramolecular carbopalladation of an allene with subsequent nucleophilic trapping of the it-allylpalladium intermediate [154].

In 1995 Grigg and co-workers reported a similar cascade consisting of an intramolecular carbopalladation and intermolecular nucleophilic trapping (Scheme 44). The regioselectivity of the aUylic nucleophilic substitution can be controlled completely by using different bases. 

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... 

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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