The organic chemistry of heterocyclic compounds containing N, O, and/or S atoms is presented. The principal topics include the preparation, physical properties, and reactivity of five- and six-membered ring systems. Total syntheses of biologically-active natural products containing heterocyclic units are discussed. The instructor sets the topic for the weekly meetings. All students are responsible for the readings and problem sets, which are based on research journals, monographs, and advanced-level textbooks. Two students give forty-five-minute oral presentations; the other students are responsible for queries, amplification, and problem sets. Format: tutorial. Evaluation is based on quality of presentations, class participation, problem sets, and a term paper on the total synthesis of a complex natural product. There are no written exams. Prerequisites: Chemistry 201-202. Enrollment limit: 4 (expected: 4).