Spatz, Julia H.; Welsch, Sebastian J.; Duhaut, David-Emmanuel; Jaeger, Nadine; Boursier, Thomas; Fredrich, Martin; Allmendinger, Lars; Ross, Guenther; Kolb, Juergen; Burdack, Christoph; Umkehrer, Michael Tetrahedron Letters, 2009 , vol. 50, # 15 p. 1705 - 1707