1. (a) Knorr, L. Ber 1883, 16, 2597. Ludwig Knorr (1859–1921) was born near Munich, Germany. After studying under Volhard, Emil Fischer, and Bunsen, he was appointed professor of chemistry at Jena. Knorr made tremendous contributions in the synthesis of heterocycles in addition to discovering the important pyrazolone drug, pyrine.
2. (b) Knorr, L. Ber 1884, 17, 546, 2032.
3. (c) Knorr, L. Ber. 1885, 18, 311.
4. (d) Knorr, L. Ann. 1887, 238, 137.
5. Burness, D. M. J. Org. Chem. 1956, 21, 97–101.