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Please login to access the full content or check if you have access via Variation 4: Carbonylative Coupling of Alkyl Halides with Organometallic Reagents

DOI: 10.1055/sos-SD-026-00532

Landais, Y.; Vincent, J. M.Science of Synthesis, (200526658.

Oxidative addition of alkyl and aryl halides to palladium(0) catalysts followed by carbonylation gives palladiumacyl complexes, which can then react in a number of ways to provide carbonyl compounds. Similarly, carbonylation of aryl halides/hexaalkyldistannane systems mediated by palladium(0) complexes affords symmetrical 1,2-diketones (Scheme 14).[‌34‌] The reaction is believed to proceed by oxidative addition of an aryl iodide to a palladium(0) complex in the presence of carbon monoxide thus generating an acylpalladium species Pd(COAr1)L2. This then undergoes transmetalation with hexaalkyldistannane to form an acyltrialkylstannane intermediate. Coupling between the latter species and the above acylpalladium Pd(COAr1)L2, followed by reductive elimination then produces the desired 1,2-diketone. As an illustration, carbonylation of 4-iodoanisole (53) under a carbon monoxide atmosphere in the presence of bis(η3-allyl)dichlorodipalladium complex gives the corresponding 1,2-diketone 54 in good yield together with a small amount of the corresponding ketone. Vinyl trifluoromethanesulfonates have been used instead of alkyl halides in a closely related palladium-catalyzed coupling reaction with (1-ethoxyvinyl)tri­methylstannane in the presence of carbon monoxide; this gives the divinyl ketone as its enol ether, which is readily hydrolyzed to the 1,2-diketone.[‌38‌] A three-component palladium-catalyzed synthesis of 1,2-diketones has been reported that involves a pentacarbonylchromate 55, a vinyl (or an aryl) iodide, and carbon monoxide. Several unsymmetrical 1,2-diketones are thus prepared in moderate to good yield; an example is shown in Scheme 14 using 1-iodo-2-phenylethene as the vinyl iodide, giving the unsymmetrical 1,2-diketone 56 as the product.[‌39‌]

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