Allene derivatives carbopalladation

A one-pot synthesis of 3,3-disubstituted indolines was achieved by taking advantage of a sequential carbopalladation of allene, nucleophile attack, intramolecular insertion of an olefm and termination with NaBPh4 (Scheme 16.6) [10]. First, a Pd(0) species reacts with iodothiophene selectively to afford ArPdl, probably because the oxidative addition step is facilitated by coordination with the adjacent sulfur atom. Second, the ArPdl adds to allene, giving a Jt-allylpalladium complex, which is captured by a 2-iodoaniline derivative to afford an isolable allylic compound. Under more severe conditions, the oxidative addition of iodide to Pd(0) followed by the insertion of an internal olefm takes place to give an alkylpalladium complex, which is transmetallated with NaBPh4 to release the product. 

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 intramolecular nucleophilic attack of a nitrogen atom on an allylpalladium complex was also used to construct a five and a six membered heterocycle in the same step. TV-substituted 2-iodobenzamides bearing an allene function in the appropriate distance from the iodine underwent cyclization through the carbopalladation of the allene moiety by the arylpalladium complex, formed in the first step of the catalytic cycle. The intermediate allylpalladium complex, part of a nine membered ring, cyclized readily to give the pyrroloisoquinolone derivative in excellent yield (4.23.). The nature of the added ligand and the solvent both had a marked influence on the efficiency of the transformation.26... 

Ma and co-workers have reported the selective synthesis of pyrrolidine derivatives through a three-component reaction based on a conceptually related strategy (Scheme 8.29) [72], Beginning with the catalytic intermolecular carbopalladation of y-allenic malonate 57 in the presence of a base, they succeeded in intercepting the internal carbonucleophile 58 with an imine such as the N-benzylidene p-toluenesulfonamide 59. The attack of the newly formed heteronucleophile on the 7r-allyl palladium intermediate affords the functionalized pyrrolidine 60 with high... 

Reaction of the o-iodoaniline derivative 431 with 1,2-decadiene in the presence of the chiral bisoxazoline 433 as a ligand and Ag salt provided the indoline 432 with 80 % ee [164], Construction of indole skeletons was carried out by intramolecular carbopalladation of allenes followed by amination. The 7r-allylpalladium intermediate 435 was formed from o-iodoaniline derivative 434, and intramolecular amination afforded the indole 436 in 89 % yield [165]. 

Efficient asymmetric carbopalladation occurred in the reaction of the racemic allene 441 with iodobenzene and malonate using BPPFOAc (Xl-14) as a chiral ligand. The chiral malonate derivative 442 with 95 % ee was obtained in 77 % yield [167],... 

Besides these alkylations of soft nucleophiles with cr-alkenylpalladium intermediates, 7T-allylpalladium complexes, formed by carbopalladation of an allene with an arylpalla-dium halide intermediate, are able to cyclize by attacking a dialkyl malonate moiety (Scheme 20)P° Instead of allenes, which give methyleneindane derivatives, cyclic and acyclic 1,4-dienes have been employed to yield tetrahydronaphthalene derivatives in good yieldsl ... 

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. 

Ma has developed a three-component allene carboamination reaction for the stereoselective synthesis of 2,5-as-disubstituted pyrrolidine derivatives [54]. A representative transformation involving allene 58, 4-iodoanisole, and imine 59 that generates 60 in 90% yield is shown below (Eq. (1.28)). The reaction is believed to proceed through the intermediate Jt-allylpalladium complex 62, which is formed by carbopalladation of the alkene to give 61 followed by addition of the malonate anion to the activated imine. Intramolecular capture of the allylpalladium moiety by the pendant nitrogen nucleophile affords the pyrrolidine product. A related asymmetric synthesis of pyrazolidines that employs azodicarboxylates as one of the electrophilic components has also been reported [55]. The pyrazolidine products are obtained with up to 84% ee when chiral bis oxazolines are employed as ligands. 

Both palladium-catalyzed carbonylative ring-forming reactions of o-iodophenols and o-iodothiophenols with allenes and carbon monoxide involve a carbopalladation step and afford l-benzopyran-4-one 47 and thiochroman-4-one 48 derivatives [61,62]. The reactions proceed in benzene at 100 °C, in autoclave at 20 atm of carbon monoxide and in the presence of Pd(OAc)2, Hiinig s base, dppb or dppf. However,... 

A variety of 3-vinyl-substituted imidazo[l,5-a]indole derivatives were synthesized by intramolecular Pd catalyzed cyclization of the indole-2-carboxylic acid al-lenamides through either a domino carbopalladation/exo-cyclization process or a novel hydroamination reaction that proceeds smoothly under microwave irradiation. Both the observed pathways involve a Tu-allyl-palladium (II) complex arising from insertion of the allene group into a palladium (II) species, the latter being formed in situ by the intervention of an aryl iodide or of the N-H group. In both these cases, the role of nucleophile is covered by the indole nitrogen (Beccalli et al., 2010). 

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