Carbopalladation intermolecular nucleophilic trapping

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

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. 

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. 

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). 

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 ... 

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