Synthesis of Diels—Alder Adducts of Phencyclone and NMR Studies of Hindered Rotations of Unsubstituted Bridgehead Phenyls: Microscale Experiments in Organic Chemistry

Abstract

Synthesis of Diels—Alder adducts of phencyclone with diverse dienophiles provides the basis for a major extended module in the second-semester laboratory of an organic chemistry course. With many accessible target compounds, students can have individual novel compounds to prepare. Especially attractive for students, the adducts are highly hindered, resulting in slow rotation about the C—C sp²—sp³ single bond to the unsubstituted bridgehead phenyl groups. Slow-exchange-limit NMR spectra (¹H at 300 MHz and ¹³C at 75 MHz) are obtained at ambient temperatures for these phenyl groups. The highly crystalline products are easily prepared and offer excellent opportunities to integrate modern 1-D and 2-D NMR techniques into this synthesis experiment, while introduccing concepts of dynamic NMR spectroscopy. The synthetic reactions are readily carried out at the microscale level.