High-Pressure Organic Chemistry. 19. High-Pressure-Promoted, Silica Gel-Catalyzed Reaction of Epoxides with Nitrogen Heterocycles1,

The reaction of epoxides with nitrogen heterocycles such as indoles, pyrroles, imidazoles, and pyrazoles was studied under both high-pressure and silica gel-catalyzed conditions. Whereas it has been reported that the treatment of indole with styrene oxide at 10 kbar and 42 °C for 24 h gave 2-(3-indolyl)-2-phenylethanol in 56% yield, the same compound was obtained in 88% yield when the reaction was conducted on silica gel at rt for 1 week. Similarly, efficient reaction of epoxides with pyrroles, imidazoles, and pyrazoles was achieved. In terms of stereochemical features, the epoxide ring opening reaction of ( R )-(+)-styrene oxide with indole was found to proceed stereoselectively in an S N 2 fashion at the benzyl carbon, in either case.