... VI.” The Cycloaddition Reaction of Cyclic Ketene- S,N—acetals with Dimethyl Acetylenedicarboxylate'” HIROKI TAKAHA'I'A, AKIRA TOMIGUCHI, Arsusm HAGIWARA, and TAKAO YAMAZAKI* Faculty of Pharmaceutical Sciences, Toyama ... H. Takahata, A. Tomiguchi, ...