Toward a Reactant Library in Template-Directed Solid-State Organic Synthesis:  Reactivity Involving a Monofunctional Reactant Based on a Stilbazole

Cocrystallization of 4-chlorostilbazole (4-Cl-sbz) with either resorcinol (res) or 4-ethylresorcinol (4-Et-res) yields three-component molecular assemblies, (res)·2(4-Cl-sbz) and (4-Et-res)·2(4-Cl-sbz), held together by two O−H···N hydrogen bonds. The olefins of each assembly conform to the distance criterion of Schmidt for [2+2] photoreaction. In the former, the olefins lie antiparallel, whereas in the latter, the olefins lie parallel. Both solids are photoactive, leading to the regiocontrolled solid-state synthesis of rctt -1,2-bis(4-pyridyl)-3,4-bis(4-chlorophenyl)cyclobutane (4-Cl-dpcb) in near or quantitative yield. The photoactivity of (res)·2(4-Cl-sbz) is attributed to the reactant undergoing a pedal-like change in conformation prior to cyclobutane formation. The ability to change the diol to achieve olefin alignment is expected to provide additional synthetic flexibility to this template approach.