Catalyzed　by　Pd-2(dba)(3)(CHCl3)-C-.　and　PPh3,　the　formal　[4+2]　cycloaddition　between　vinyl　benzoxazinones　and　oxazol-5-(4H)-ones　proceeded　readily　and　delivered　3,4-disubstituted　dihydro-2(1H)-quinolinones　in　the　reasonable　chemical　yields　with　excellent　diastereoselectivities.　The　relative　stereochemical　configuration　of　the　title　products　was　unambiguously　characterized　with　the　use　of　X-ray　diffraction　analysis.