A Novel Synthesis of [1]Benzothieno[3,2-b][1]benzofuran

Abstract

A new synthesis of the title compound based on the formation of the furan ring in the key step was elaborated. Methyl 2-methoxy[1]benzothieno [3,2-b][1]benzofuran-7-carboxylate (15) was prepared by this methodology as a new type of a core for liquid crystal synthesis. Synthesis and reactivity of [1]benzothieno[3,2-b]furan and thieno[3,2-b]-[1]benzofuran has been extensively investigated in the last years 1-3 . It was shown that [1]benzothieno[3,2-b]furan and its vinyl derivatives can be used 4,5 in Diels-Alder reactions for construction of a new benzofused heterocyclic system -[1]benzothieno[3,2-b][1]benzofuran (1), the reactivity of which was also reported 6 . General disadvantages of the studied cycloadditions involve high reaction temperatures, long reaction times, lower yields and the necessity to use the sealed-tube technique. Side reactions as a result of consecutive cycloaddition reactions also complicated syntheses of the ring system 1 and its derivatives. The design and synthesis of new types of liquid crystalline materials is an important area, as it can supply target molecules for the mesophase behaviour investigation. Recently, we introduced 7,8 the thieno[3,2-b]furan skeleton as a new type of heteroaromatic core for construction of new ferroelectric liquid crystals. That is why an effective synthesis of dibenzofused system 1 for creating a core of new liquid crystals was the aim of our following studies. In this paper, we wish to report the results of development of a general synthesis of 1 as well as its unsymmetrically disubstituted derivative 15.Retrosynthetic disconnection (Scheme 1) of the parent heterocyclic system of 1 led to a key intermediate: a 2-(2-sulfanylphenyl)[1]benzofuran 2, possessing a thiol group (X = SH) or a precursor group in position 2 of the phenyl ring. Formation of the thiophene ring could be achieved 9-13 by an

Electrochemical Synthesis of Thienoacene Derivatives: Transition‐Metal‐Free Dehydrogenative C−S Coupling Promoted by a Halogen Mediator

“…The reaction with 1.0 equivalent of Br 2 instead of NBS gave 3 a quantitatively. Further addition of Br 2 (2.0 equiv) gave 2 a in 87 % yield . We also tried to use n Bu 4 NBr 3 , and found that 2 a was obtained quantitatively, while a stoichiometric amount of n Bu 4 NBr 3 was required.…”