Cascade Aza-Prins/Friedel-Crafts Reaction of Homocinnamyloxycarbamate and Aromatic Aldehydes Yielding Aromatic Ring-Annulated Hydrocyclopenta-1,2-oxazinane

The cascade aza-Prins/Friedel-Crafts reaction of homocinnamyloxycarbamate with electron-rich aromatic aldehydes has been successfully established. Most of the aromatic aldehydes react with the carbamate stereoselectively to generate cis-hydroindeno-1,2-oxazinanes. However, the cascade reactions of benzaldehydes bearing two methoxy groups at the meta-positions exhibit a unique stereochemical profile. Furthermore, the cascade reaction of benzaldehyde bearing three methoxy groups at the meta- and para-positions proceeds along with a skeletal rearrangement. Additionally, the aza-Prins/Ritter reaction of cinnamyloxycarbamate with various aldehydes was found during the development of the cascade reaction. In contrast to the cascade aza-Prins/Friedel-Crafts reaction, the aza-Prins/Ritter reaction gave trans-disubstituted isoxazolidines. These stereochemical profiles for both reactions were considered on the basis of several transition-state models.