... Rf-values, the already known compounds III and IV, together with VII, II and I. Physical and chemical data are ... 4a) R. Hazard, J. Cheymol, P ... Ltd., 1969, p. 164; (b) AR Katritzky and Ambler, "Physical Methods in Heterocyclic Chemistry", Academic Press, New York, NY, 1963, p. 161 ...