The first synthesis of lupinacidins A and B, tumor cell invasion inhibitors of microbial origin, has been achieved in four operational steps from 3-methoxy-2-methyl-2-cyclohexenone via the Diels–Alder cycloaddition of a conjugated cyclohexadiene derivative with a juglone-derived sulfinyl quinone followed by sequential elimination of a sulfenic acid and ethylene to afford protected forms of the target molecules.