... and the residue was purified by column chromatography. Received: April 18, 1997 [210365IE] German version: Angeu. Chem. ... 2344 0 WILEY-VCH Verlag GmbH, D-69451 Weinheim. 1997 0570-0833/97/3621-2344 S 17 SO+ 5OjO Angew Chem Inr Ed Engl 1997, 36, No 21