Acylpalladium derivatives intramolecular reactions

Carboxylic acid chlorides and chloroformate esters add to tetrakis(triphenylphosphine)palladium(0) to form acylpalladium derivatives (equation 42).102 On heating, the acylpalladium complexes can lose carbon monoxide (reversibly). Attempts to employ acid halides in vinylic acylations, therefore, often result in obtaining decarbonylated products (see below). However, there are some exceptions. Acylation may occur when the alkenes are highly reactive and/or in cases where the acylpalladium complexes are resistant to decarbonylation and in situations where intramolecular reactions can form five-membered rings. 

C. INTRAMOLECULAR REACTIONS OF ACYLPALLADIUM DERIVATIVES WITH ENOLATES... 

Both intennolecular and intramolecular reactions of acylpalladium derivatives with enolates have been shown to be highly general reactions over the last dozen or so years. 

Bromobenzyl alcohol and its derivatives were converted to phthalides by the palladium catalysed insertion of carbon monoxide and intramolecular quenching of the formed acylpalladium complex. 2-Hydroxymethyl-1-bromonaphthaline, for example, gave the tricyclic product in excellent yield (3.34.). An interesting feature of the process is the use of molybdenum hexacarbonyl as carbon monoxide source. The reaction was also extended to isoindolones, phthalimides and dihydro-benzopyranones 42... 

The ability of the in situ generated aqflpalladium complexes to activate carbon-carbon triple bonds toward intramolecular nucleophilic attack emerged as a valuable tool for the synthesis of functionalized heterocycle derivatives (Scheme 9.28). The reaction is considered to proceed through the intramolecular regioselective nucleophilic attack across the carbon-carbon triple bond activated by coordination to the acylpalladium complex, followed by a reductive elimination step that produces the functionalized cyclic derivative and regenerates the catalytic species. 

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