Carbopalladation intermolecular trapping

Using trimethylsilyl-substituted vinyl bromides, the carbopalladation-intermolecular trapping protocol afforded trimethylsilyl-substituted 1,3-dienes 30/31 and 2-alkenyl-aIlyl silane 32, which could be used for further elaboration (Scheme 13). ... 

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). 

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 ... 

Two types of reactions are summarized in this section (i) the intermolecular carbopalladation leads to a Pd functionality such as alkyl-, alkenyl-, or allylpalladium complexes, which is intramolecularly trapped by a heteroatom (again Wacker-type processes are mechanistic alternatives) (ii) the palladium catalyst is not directly involved in the hetero-cyclization step, but the carbopalladation builds up a suitable functionality or changes bond angles so that the heterocyclization can take place. 

Over the last fifteen years or so the domino process involving the intermolecular and intramolecular carbopalladation of alkynes followed by trapping of the resultant... 

In contrast to the diverse insertion chemistry of vinylpalladium intermediates discussed in Sects. IV.3 and IV.5, the reactions of vinylpalladium complexes with electrophiles had not been reported until recently. Although a single report on the annulation of the o-mer-curio benzaldehyde with diphenylacetylene into the corresponding indenols and inde-nones catalytic in palladium and stoichiometric in copper had been communicated in 1992, the more synthetically useful protocol for the catalytic version of this type of transformation remained unknown until 1999. In this section the intermolecular carbopalladation of alkynes with aryl halides followed by the intramolecular trapping of the formed vinylpalladium species with ketones, aldehydes, and nitriles will be discussed. 

Cascade intermolecular carbopalladations of alkynes followed by intramolecular trapping with electrophiles represent not only a novel type of organic transformation involving vinylpalladium intermediates, but also provide synthetically useful routes toward differently substituted indenols, indanones, indenones, and naphthy-lamines." Although these protocols are restricted to the intramolecular trapping with electrophiles, a wide application of this methodology toward the synthesis of various types of complex carbocychc compounds may be anticipated in the near future. 

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. 

Intermolecular carbopalladation of a triple bond as in 457 by an in sitw-formed organopalladium triflate and subsequent intramolecular nucleophibc trapping gives rise to indoles 458 (Scheme 8.86) [600]. The versatihty of this approach derives from the fact that the triflate may be varied in a wide range. 

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