Hetero-Diels--Alder Reaction of Phosphinyl and Phosphonyl Nitroso Alkenes with Conjugated Dienes: An Aza-Cope Rearrangement.

Phosphorylated nitroso alkenes react with cyclic dienes such as cyclopentadiene or cydohexadiene to afford hetero Diels--Alder-type cydoadducts where the nitroso alkene participates as dienophile component and the cyclic olefin acts as the 4π-electron (diene) system. Subsequent aza-Cope re-arrangement affords highly functionalized 5,6-dihydro-4H-1,2-oxazines. Conversely, the reaction of TMS-substituted cyclopentadiene (dienophile) with nitroso alkenes as heterodienes leads directly to bicyclic 1,2-oxazines. Theoretical studies are in agreement with the experimental results and with the new aza-Cope rearrangement proposed. [ABSTRACT FROM AUTHOR]