Irradiation of crystalline charge transfer complex 3 formed between (S)-(+)-2-(6-methoxy-2-naphthyl)propanoic acid 1 and 1,2,4,5-tetracyanobenzene 2 is shown to lead to the optically active decarboxylated-coupled product (+)-4 in high yield and substantial enantiomeric excess. In this process the configuration of the stereogenic carbon in 1 is retained to some extent by the control of the crystal lattice. The factors which affect the reaction of the molecular crystals were also examined. The relationship between the reactivity and the crystal structure is discussed.