Diels–Alder reactions of N-sulfonyl substituted aza-ortho-xylylenes generated from the corresponding 1,4-dihydro-2H-3,1-benzoxazin-2-one derivatives

Abstract

N-Tosyl- and N-alkylidene-sulfonyl substituted 1,4-dihydro-2H-3,1-benzoxazin-2-ones 2c-g easily undergo thermal carbon dioxide extrusion leading to the aza-ortho-xylylenes 3c–g. The intermediates 3c,d can be trapped by electron-poor ethylenic and acetylenic dienophiles, giving tetrahydroquinoline and quinoline derivatives. The reactions of 2c with non-symmetrical dienophiles are completely regioselective. N-Alkylidenesulfonyl substituted aza-ortho-xylylenes 3f–g undergo intramolecular Diels–Alder reactions leading to the tricyclic compounds 10 and 11, while the aza-ortho-xylylene generated from 4-(hex-5-enyl)-N(4-methylphenylsulfonyl)-1,4-tetrahydro-2H-3,1-benzoxazin-2-one undergoes a [1,5] hydrogen shift leading to N-[2-(1E)-hepta-1,6-dien-1-ylphenyl]-4-methylbenzenesulfonamide.