Issue 24, 2006

Insights into the mechanism of the site-selective sequential palladium-catalyzed cross-coupling reactions of dibromothiophenes/dibromothiazoles and arylboronic acids. Synthesis of PPARβ/δ agonists

Abstract

A reactivity study, aided by NMR spectroscopy, allowed a mechanistic rationale to be postulated for the palladium-catalyzed regioselective coupling of arylboronic acid (and arylstannane where feasible) at the position next to the sulfur atom in functionalized dibromothiophenes and dibromothiazoles. The analysis of the NMR spectra (using 19F from the boronic acid CF3 group and 31P from the phosphine of the catalyst as probes) of the entire reaction starting from the dibromoheterocycles allowed the qualitative proposal that the transmetalation is the rate-limiting step for both sequential substitution processes. The extremely facile oxidative addition at the C–Br bond next to the sulfur atom of the heterocycle instead determines the positional selectivity. An additional Stille reaction then replaced the second halogen, providing the trisubstituted heterocyclic scaffolds of PPAR ligands, which displayed PPARβ/δ agonist activity, as revealed by reporter assays in living cells.

Graphical abstract: Insights into the mechanism of the site-selective sequential palladium-catalyzed cross-coupling reactions of dibromothiophenes/dibromothiazoles and arylboronic acids. Synthesis of PPARβ/δ agonists

Supplementary files

Article information

Article type
Paper
Submitted
24 Aug 2006
Accepted
26 Oct 2006
First published
13 Nov 2006

Org. Biomol. Chem., 2006,4, 4514-4525

Insights into the mechanism of the site-selective sequential palladium-catalyzed cross-coupling reactions of dibromothiophenes/dibromothiazoles and arylboronic acids. Synthesis of PPARβ/δ agonists

R. Pereira, A. Furst, B. Iglesias, P. Germain, H. Gronemeyer and A. R. de Lera, Org. Biomol. Chem., 2006, 4, 4514 DOI: 10.1039/B612235C

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