The angular benzobisthietes 3 and 5 could be prepared by synthetic sequences in which the final step was in both cases a twofold dehydration of the corresponding bis(hydroxymethyl)dimercaptobenzenes 10 and 14, respectively. Flash vacuum pyrolysis conditions were used for the generation and isolation of 3 and 5 which are highly reactive bisdiene systems. Cycloaddition reactions with the dienophiles 15 and 18a,b led to the adducts 16, 17, and 19a,b. (C) 1998 Elsevier Science Ltd. All rights reserved.