Diels-Alder Reactions of a Styrene-Isocyanate: Unexpected Formation of a Pyridinone and Uracil

During the preparation of 6-bromoisoquinolinone, a novel and unexpected reaction occurred to form a pyridinone and a pyrimidine-2,4-dione. We propose a [4+2] Diels-Alder dimerization of an intermediate styrene-isocyanate to explain the observed products.