Lewis acid catalyst. Prepn: S. Singh et al., Indian J. Chem. 22A, 814 (1983); M. Labrouillère et al., Tetrahedron Lett. 40, 285 (1999). Catalysis of large scale acetylations of alcohols and diols: M. D. Carrigan et al., Synthesis 2001, 2091; of Biginelli Reaction: R. Varala et al., Synlett 2003, 67; of epoxide opening with aromatic amines: T. Ollevier, G. Lavie-Compin, Tetrahedron Lett. 45, 49 (2004). Review as catalyst for acylations and sulfonylations: C. Le Roux, J. Dubac, Synlett 2002, 181-200; brief review of catalytic use in a variety of organic reactions: S. Antoniotti, ibid. 2003, 1566-1567.