Palladium-Catalyzed Nucleophilic Substitution and Alkylation

An important industrial process based on Pd-alkene complexes is the Wacker reaction, a catalytic method for conversion of ethylene to acetaldehyde. The first step is addition of water to the Pd-activated alkene. The addition intermediate undergoes the characteristic elimination of Pd(0) and H+ to generate the enol of acetaldehyde. 

The reaction is run with only a catalytic amount of Pd. The co-reagents CuCl2 and 02 serve to reoxidize the Pd(0) to Pd(II). The net reaction consumes only alkene and oxygen. 

When the Wacker condition are applied to terminal alkenes, methyl ketones are formed.82 

The allylation reaction has also been used to form rings. /i-Sulfonyl esters have proven particularly useful in this application for formation of both medium and large rings.88 In some cases, medium-sized rings are formed in preference to six- and seven- 

The sulfonyl substituent can be removed by reduction after the ring closure (see Section 

7r-Allyl palladium species are involved in a number of useful reactions which result in allylation of nucleophiles. This reaction can be applied to carbon-carbon bond formation with relatively stable carbanions, such as those derived from malonate esters and j5-sulfonyl esters. The 7r-allyl complexes are usually generated in situ by reaction of an allylic acetate with a catalytic amount of tetrakis(triphenylphosphine)palladium. The 

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