Furyl sulfonamides

Amides and sulfonamides undergo intramolecular chemistry to form aryl amides and aryl sulfonamides (Equations (17)—(19)) in the presence of palladium catalysts ligated by arylphos-phines.35,89 Initially, complexes of P(furyl)3 and P(o-tol)3 were most effective catalysts, but complexes of Hayashi s MOP and van Leeuwen s DPEphos and xantphos have lately been shown to be more active.90 In the presence of catalysts containing one of these ligand systems, five-, six-, and seven-membered rings were formed from halogenated benzamides or from substrates containing an acetamide, an A-carbobenzyloxy, or a t-butylcarbamate substituent tethered to the aryl halide (Equations (18) and (19)) ... 

However, studies on the scope of this sequence revealed that the substrate has to be an N-tosyl sulfonamide and that certain boronic acids are not trans-metallated but rather give rise to the formation of the pyrrole 21 or a pyridine derivative 22 (Scheme 7). The peculiar outcome as a carbopalladation-Suzuki sequence is rationalized by co or dinative stabilization of the insertion intermediate 18 by the sulfonyl oxygen atom, as represented in structure 19, now suppressing the usual /3-hydride elimination. If the transmetallation is rapid the Suzuki pathway is entered leading to product 17. However, if the transmetallation is slow, as for furyl or ferrocenyl boronic acid, either /i-hydride elimination or a subsequent cyclic carbopalladation occurs. The former leads to the formation of the diene 20 that is isomerized to the pyrrole 21. The latter furnishes the cyclopropylmethyl Pd species 23, which rearranges with concomitant ring expansion to furnish piperidyl-Pd intermediate 24 that suffers a -hydride elimination to give the methylene tetrahydro pyridine 22. 

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