Symmetrically and unsymmetrically substituted diarylcyclobutenes
are synthesized in 20-70% yields from alkyne precursors
via cobalt-catalyzed [2+2] cycloadditions.
The reactions proceed under mild conditions and provide access to
differently substituted diarylethene derivatives. All the diarylcyclobutene products
undergo reversible photoisomerization upon irradiation with UV/Vis
light. The ring-closed isomers show different thermal stabilities
towards reisomerization with half-lives ranging from 9 to 300 hours.
diarylethene - photoswitchable - cyclobutene - photochromic reactions - [2+2] cycloaddition