BIS(2-THIENYL)ETHYLENE GIVES CYCLOADDUCTS BY RADICAL ION PAIRS
1,1-Bis(2-thienyl)ethanol reacts at room temperature in the absence of light with electron-deficient alkenes such as TCNE or DDQ to give quantitatively cycloadducts derived from 1,1-bis(2-thienyl)ethylene.The process was monitored by esr and it is shown that it is the first example of a cycloaddition involving a heterocyclic ring that occurs through the formation of intermediate radical ion pairs.Fragmentation of the DDQ adduct constitutes a straightforward new route to the 4,5-dicyanobenzothiophene skeleton.