Bruce H. PMID:24278086 Lipshutz and Bryan A. Frieman from the University of California, Santa Barbara, have made investigations on [{(R)-(-)-DTBM-segphos}CuH] as a hydrosilylation reagent regarding stability and preparation (Angew. 1450752-97-2 Formula Chem. Int. Ed. 2005, 44, 6345. DOI: 10.1002/anie.200500800). This reagent proved to be very stable over several weeks at room temperature (no decrease in ee´s) if prepared by using Cu(OAc)2∙H2O as copper source, and stored as stock solution in a bottle. 1380300-88-8 Data Sheet Excellent ee´s and good conversions were obtained in several asymmetric hydrosilylations at room temperature, but also microwave heating could be applied for the reduction of enone 1. By using a substrate/catalyst ratio (S/C) of 1000:1, the reaction time could be reduced from several hours to only 10 minutes.
Glycosylations
Knud J. Jensen and co-workers from the Royal Veterinary and Agricultural University, Denmark, have described the microwave promoted synthesis of oligosaccharides (Org. Biomol. Chem. 2005, 3, 3966. DOI: 10.1039/b511266d). Without the use of a strong Lewis acid, O-glycosylations could be accelerated from up to 31 hours to 5-40 minutes by applying microwave heating. Glycosylation reactions have been performed with trichloroacetimidate (2) or DISAL (3,5-dinitrosalicylate, 1) donors, respectively, in the latter case with α-selectivity for sterically hindered alcohols.
Synthesis of 3-Aminoimidazo[1,2-a]Pyridines
A novel one-step three-component reaction for the synthesis of 3-aminoimidazo[1,2-a]pyridines has been demonstrated by the group of Christopher Hulme from Eli Lilly and Company (Tetrahedron Lett. 2005, 46, 8355. DOI: 10.1016/j.tetlet.2005.09.181). In this multicomponent reaction, an aminopyridine1, aldehyde 2 and TMS-CN (3) are reacted under microwave heating to give the desired products 4. By using TMS-CN as non-classical isonitrile equivalent, no further deprotection steps were necessary, making this method applicable for library synthesis.
Cross-Metathesis Reactions
In a recent publication Frédéric C. Bargiggia and William V. Murray from Johnson & Johnson Pharmaceuticals have reported on cross-coupling Metathesis between deactivated olefins (J. Org. Chem. 2005, 70, 9636.DOI: 10.1021/jo0514624). By applying microwave irradiation, reaction rates could be enhanced compared to classical heating, showing superior yields for the Hoveyda-Grubbs catalyst 1 than for 2nd generation Grubbs´ catalyst. No differences in yields or selectivities in homo- or hetero couplings, respectively have been observed by comparison studies of microwave- and oil-bath heating.
