Nucleophiles reaction with organopalladium

These rc-allyl complexes are electrophilic in character and undergo reaction with a variety of nucleophiles. After nucleophilic addition occurs, the resulting organopalladium intermediate usually breaks down by elimination of Pd(0) and H+. 

Further development of termination strategies has led to the use of allenes, which trap the organopalladium intermediate to give 7r-allylic complex. The latter undergoes facile reactions with nucleophiles. The overall process becomes a pentamolecular cascade (Scheme 17). 

For Pd-catalyzed cross-coupling reactions the organopalladium complex is generated from an organic electrophile RX and a Pd(0) complex in the presence of a carbon nucleophile. Not only organic halides but also sulfonium salts [38], iodonium salts [39], diazonium salts [40], or thiol esters (to yield acylpalladium complexes) [41] can be used as electrophiles. With allylic electrophiles (allyl halides, esters, or carbonates, or strained allylic ethers and related compounds) Pd-i73-jt-allyl complexes are formed these react as soft, electrophilic allylating reagents. 

Acemoglu L, Williams JMJ (2002) Synthetic Scope of the Tsuji-Trost Reaction with Allylic Halides, Carboxylates, Ethers, and Related Oxygen Nucleophiles as Starting Compounds. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1689... 

Another interesting tandem Michael initiated sequence was developed in our laboratory by combining the conjugate addition of unsaturated alkoxides to alkylidene malonates with a palladium-mediated coupling reaction with an organic halide. In this cydization reaction, an organopalladium species acts as the electrophilic partner of the cydization. This reaction results in the trans addition of the organopalladium species and of the nucleophile across the unsaturation, and therefore, in overall difunctionalization of the unsaturated substrates [66,67]. 

Fauvarque, J. F., Jutand, A. Reaction of various nucleophiles with organopalladium compounds. Bull. Soc. Chim. Fr. 1976, 765-770. 

Organopalladium intermediates are also involved in the synthesis of ketones and other carbonyl compounds. These reactions involve acylpalladium intermediates, which can be made from acyl halides or by reaction of an organopalladium species with carbon monoxide. A second organic group, usually arising from any organometallic reagent, can then form a ketone. Alternatively, the acylpalladium intermediate may react with nucleophilic solvents such as alcohols to form esters. 

Carbopalladation occurs with soft carbon nucleophiles. The PdCl2 complex of COD (100) is difficult to dissolve in organic solvents. However, when a heterogeneous mixture of the complex, malonate and Na2C03 in ether is stirred at room temperature, the new complex 101 is formed. This reaction is the first example of C—C bond formation and carbopalladation in the history of organopalladium chemistry. The double bond becomes electron deficient by the coordination of Pd(II), and attack of the carbon nucleophile becomes possible. The Pd-carbon n-bond in complex 101 is stabilized by coordination of the remaining alkene. The carbanion is generated by treatment of 101 with a base, and the cyclopropane 102 is formed by intramolecular nucleophilic attack. Overall, the cyclopropanation occurs by attack of the carbanion twice on the alkenic bond activated by Pd(II). The bicyclo[3.3.0]octane 103 was obtained by intermolecular attack of malonate on the complex 101 [11]. 

The lithium salt of indole can be alkylated or vinylated by ethylene complexed with PdCl2. These reactions follow patterns established for Pd-catalyzed addition of many other nucleophiles and presumably involve an organopalladium intermediate which can either undergo elimination to form the N-vinylindole or reduction to give the N-ethylindole as shown in Scheme 21 (81JOC2215). Although at the present time this procedure would seldom be competitive with the use of SN2 conditions for alkylation, the development of vinylation conditions which were catalytic in Pd might be useful. 

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