Palladium catalysis aryne reactions

We reported that the palladium-catalyzed reaction of arynes with bis-jr-allyl palladium complex afforded 1,2-diallylated derivatives of benzene in good yields (Scheme 32) [77]. The reaction of 104 with allyltributylstan-nane 3a and allyl chloride 11 in acetonitrile in the presence of 2.5 mol % Pd2(dba)3.CHCl3/dppf catalyst at 40 °C for 12 h afforded 1,2-diallyl benzene 105 in 76% yield. The generation of benzyne 106 takes place presumably first from 104 under the conditions of the palladium catalysis, which reacts with the complex 2 in a manner similar to the diallylation of activated olefins (refer Scheme 29). 

In this chapter we described [2 + 2 + 2] and related cycloaddition reactions using palladium, iron, manganese, rhenium, and other transition metals. Palladium complexes are able to catalyze [2 + 2 + 2] and related cycloaddition reactions, which proceed via cascade-type mechanism or metallacycle intermediates. It is worthy of note that arynes are suitable substrates for this palladium catalysis. Iron complexes are promising catalysts for practical [2 + 2 + 2] cycloaddition reactions, owing to their low cost and nontoxicity, although both catalytic activity and substrate scope are not satisfactory. Manganese and rhenium complexes allow the use of 3-keto esters as a cycloaddition partner. To realize the practical process and broaden the product scope, further development of new transition-metal catalysts is expected in this research field. 

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