Methine‐Brigded Five‐Membered Heterocycles as Precursors for Low‐Gap Polymers

The synthesis of suitable precursors of polyarenemethines (PAM) 1, which are predicted to be potential low gap polymers, is described. The Knoevenagel condensation of heteroaromatic aldehydes with 2,5‐dihydrothiophene 1,1‐dioxide (5), 2,5‐dihydrothiophene 1‐oxide (9), and its benzo‐annulated analogs [6 and [10] yields the methine‐bridged compounds 7, [8], 11, and [12], respectively. Reduction of the methine‐bridged sulfoxides 11 and [12] leads to the corresponding sulfides 13 and [14]. For compound 18 with a high sterical demand another route has been developed. Thus, the reaction of the dicarbinol 17 with HI yields directly the heteroaromatic quinodimethane 18. The molecular structures of 7a and 18 are determined by X‐ray analysis.