Braddock DC, Hii KKM, Brown JM1998Journal article Journal:ANGEWANDTE CHEMIE-INTERNATIONAL EDITIONVolume:37Issue:12, pp.1720 - 1723No abstract availableKeywords:cyclizations , isotopic labeling , Lewis acids , NMR spectroscopy , reaction mechanisms DOI10.1002/(SICI)1521-3773(19980703)37:12<1720::AID-ANIE1720>3.0.CO;2-W