Oxanorbornadienes (ONDs) undergo facile Michael addition with thiols and then fragment by a retro-Diels−Alder (rDA) reaction, a unique twostep sequence among electrophilic cleavable linkages. The rDA reaction rate was explored as a function of the furan structure, with substituents at the 2-and 5positions found to be the most influential and the fragmentation rate to be inversely correlated with electron-withdrawing ability. Density functional theory calculations provided an excellent correlation with the experimentally measured OND rDA rates.

Azanorbornadienes (ZNDs), prepared from pyrroles, undergo Michael reaction with thiols followed by retro-Diels−Alder (rDA) cleavage to release the starting pyrrole and a thiomaleate. Somewhat less reactive in this regard than furan-derived oxanorbornadienes, ZNDs have an additional point of variability at the pyrrole nitrogen center. Sulfonylated ZNDs were far more stable toward rDA cleavage than acylated analogues. tert-Butoxycarbonyl examples were much less reactive with thiols, rendering the rDA step slower than the initial conjugate addition.