The isolation of thiirane 1-imides was achieved via imination of anti-and syn-9,9'-bibenzonorbornenylidene sulfides by Chloramine T at room temperature, followed by crystallization of the reaction mixture at -18 degrees C. Allowing CD2Cl2 solutions of the thiirane 1-imides stand at room temperature or heating their crystals to around 120 degrees C led to the formation of the corresponding 1, 2-thiazeti dines with retention of the configuration of the thiirane 1-imides.