Oxaziridines

Advances in the Chemistry of Oxaziridines

“…Oxaziridines participate in a remarkably broad variety of rearrangement reactions when exposed to exogenous chemical and photochemical stimuli. Acid-mediated rearrangements to hydroxylamines, base-catalyzed eliminations, thermal rearrangements to nitrones, and photochemical isomerizations have all been extensively studied and reviewed . In addition, the Aubé group elegantly demonstrated the synthetic utility of photochemical isomerizations of oxaziridines in their synthesis of the yohimbine alkaloids …”

Controlling Selectivity for Cycloadditions of Nitrones and Alkenes Tethered by Benzimidazoles: Combining Experiment and Theory

“…[4c,19] Additional heating at a higher temperature (120 °C, EtOH, µw, 45 minutes) led to the rearrangement of the nitrone functional group to an amide (and to a lesser amount of an ester; Figure 2). [20,21] Moreover, when the R 1 = t Bu, R 2 = R 3 = H, R 4 = c Hex system (Table 1, entry 9) was subjected to the usual reaction conditions, no cycloadducts were isolated (the importance of the R 1 and R 4 substituents are discussed below). NMR data (see Supporting Information) suggested that a nitrone was formed but again did not react further, and additional heating at a higher temperature again led to an amide product (the same is true for the terminal alkyne analog of the system shown in Figure 2; see Supporting Information).…”

“…Our calculations on a small model system (Scheme 3) suggest that simple rotation about the C=N bond (we were unable to locate any transition state structure for such a process) or formation of a diradical or oxaziridine intermediate under thermal conditions (barriers for each of >50 kcal/mol) are unlikely (photochemical generation of such species cannot be definitively ruled out for our reaction conditions). [20,21,24] Scheme 4 shows an experiment that suggests another possible pathway for isomerization. A nitrone with R 4 = Me but not bearing an alkene was synthesized ( Z:E ::3:1 in DMSO- d 6 ; Z:E ::1.1:1 in benzene- d 6 ) [25a] and subjected to the usual reaction conditions for cycloaddition in the presence of a hydroxyl amine with a different R 4 group ( c Hex).…”