Fluorous Suzuki-Type Coupling Reactions

A recent publication by Wei Zhang and co-workers from Fluorous Technologies (Org. Lett. 2004, 6, 1473. DOI) describes a new strategy to improve the efficiency of Suzuki coupling reactions by combining rapid microwave synthesis with fluorous separation techniques (F-SPE). Aryl perfluorooctylsulfonates 1 as precursors for Suzuki-type couplings were readily prepared from phenols and commercially available perfluorooctylsulfonylfluoride. Subsequent Suzuki reaction with aryl boronic acids in the presence of a suitable Pd catalyst provided the desired biaryls 2 in high yield. Work-up simply involved filtration of the reaction mixture through a fluorous solid-phase extraction cartridge (F-SPE).

Resin-Bound Dienophile Scavengers

Xiaoguang Lei and John A. Porco Jr. of Boston University have demonstrated (Org. Lett. 2004, 6, 795. DOI) the usefulness of a thermally stable polymer-supported anthracene derivative (i.e. 3) for scavenging dienophiles under microwave conditions. This strategy was successfully used to rapidly sequester reactive dienophiles from reaction mixtures containing flavonoid Diels-Alder cycloadducts (e.g. 5) prepared by microwave-assisted Diels-Alder cycloaddition from flavonoid dienes (e.g. 4).

One-Pot Imidazole Synthesis

A simple, high yielding synthesis of 2,4,5-trisubstituted imidazoles of type 6 from 1,2-diketones and aldehydes in the presence of ammonium acetate was recently reported by Scott E. Wolkenberg and co-workers from Merck (Org. Lett. 2004, 6, 1453. DOI). Utilizing microwave irradiation, alkyl-, aryl-, and heteroaryl-substituted imidazoles are formed in very high yields ranging from 76-99%. Further microwave-assisted alkylation of 2,4,5-trimethylimidazole with benzyl chloride in the presence of base led to the alkaloid lepidiline B in 43% overall yield.

Preparation and Reactions of Cyclic Thioureas

Eric Wellner and co-workers from Active Biotech AB have made extensive use of microwave chemistry in the preparation of cyclic thioureas and guanidines (J. Org. Chem. 2004, 69, 1571. DOI). Utilizing MAOS it was possible to assemble all intermediates and target molecules without any need of activation or protecting groups, cutting reaction- and workup times to a minimum.

Books written by Highlight Authors:

Douglass F. Taber

C. Oliver Kappe