1. For excellent reviews, see e.g.: (a) Comprehensive Heterocyclic Chemistry; Katritzky, A. R.; Rees, C. W.; Boulton, A. J.; McKillop, A., Eds.; Pergamon Press: Oxford, 1984; Vol. 2;
2. (b) Toomey, J. F.; Murugan, R. In Progress in Heterocyclic Chemistry; Suschitzky, H.; Scriven, E. F. V., Eds.; Pergamon Press: Oxford, 1994; Vol. 6, p. 206.
3. For reviews, see e.g.: (a) Plunkett, A. O. Nat. Prod. Rep. 1994, 11, 581–590;
4. (b) Wang, C. L. J.; Wuonola, M. A. Org. Prep. Proc. Int. 1992, 24, 585;
5. (c) Pinder, A. R. Nat. Prod. Rep. 1992, 9, 491–504;