Direct Generation of N‐Alkoxycarbonyl Nitrones from Oximes: Intramolecular Cycloaddition of Oximes Having Alkene Moieties

Abstract

δ,ε‐Unsaturated oximes, on heating with O‐alkyl S‐(pyridin‐2‐yl)carbonothioates (PySCO<sub>2</sub>R) in refluxing toluene, undergo intramolecular cycloaddition to give N‐alkoxycarbonylated multi‐cyclic compounds. Mechanistic studies indicate that the reaction involves direct generation of N‐alkoxycarbonyl nitrones followed by cycloaddition, instead of intramolecular oxime‐olefin cycloaddition (IOOC) followed by alkoxycarbonylation. DFT calculation indicates that N‐alkoxycarbonylation of oxime with PySCO<sub>2</sub>R is a concerted reaction. The reaction of oxime with a chiral alkoxycarbonylation reagent exhibits a reasonably high diastereo‐face selectivity.

Intermolecular 1,3‐Dipolar Cycloaddition Reaction of N‐Carbamoyl Nitrones Generated by N‐Selective Carbamoylation of Oximes with Isocyanates

“…The Boc group has also recently attracted attention as a substituent that can be deprotected without reduction [4] . We have reported intramolecular cycloadditions of N ‐alkoxycarbonyl nitrones, including N ‐Boc nitrones generated by N‐selective acylation of oxime with PySBoc (Scheme 1b, 1c‐i) [5] . Given that the O−H bond and lone pair on nitrogen in an oxime lie in the same plane, a hetero allene such as isocyanate should be a suitable acylating reagent, because it has a lone pair as a hydrogen–acceptor and a p orbital as an acceptor of the electron pair in the same plane.…”