Expanding the versatility of trihalophenols as molecular templates to achieve a series of [2+2] cycloaddition reaction involving 1,2-bis(2-pyridyl)ethylene

Abstract

A series of [2+2] cycloaddition reactions involving trans-1,2-bis(2-pyridyl)ethylene that is templated by three 2,4,6-trihalophenols is reported. In each case, the co-crystal undergoes a quantitative and stereoselective photoreaction to generate the corresponding cyclobutane, namely rctt-tetrakis(2-pyridyl)cyclobutane. The reliability of these phenols to engage in the combination of homogenous and face-to-face π–π stacking interactions along with O–H⋯N hydrogen bonds places the carbon–carbon double bond within the reactant in a suitable position to photoreact. In addition, density functional theory calculations supported the occurrence of the homogeneous stacking pattern which is required to form these photoreactive co-crystals.