Straightforward Synthesis of 2- and 2,8-Substituted Tetracenes

Abstract

A simple regiospecific route to otherwise problematic substituted tetracenes is described. The diverse cores (E)-1,2-Ar¹ CH₂ (HOCH₂ )C=C(CH₂ OH)I (Ar¹ =Ph, 4-MePh, 4-MeOPh, 4-FPh) and (E)-1,2-I(HOCH₂ )C=C(CH₂ OH)I, accessed from ultra-low cost HOCH₂ C≡CCH₂ OH at multi-gram scales, allow the synthesis of diol libraries (E)-1,2-Ar¹ CH₂ (HOCH₂ )C=C(CH₂ OH)CH₂ Ar² (Ar² =Ph, 4-MePh, 4-iPrPh, 4-MeOPh, 4-FPh, 4-BrPh, 4-biphenyl, 4-styryl; 14 examples) by efficient Negishi coupling. Copper-catalysed aerobic oxidation cleanly provides dialdehydes (E)-1,2-Ar¹ CH₂ (CHO)C=C(CHO)CH₂ Ar² , which in many cases undergo titanium(IV) chloride-induced double Bradsher closure, providing a convenient method for the synthesis of regiochemically and analytically pure tetracenes (12 examples). The sequence is typically chromatography-free, scalable, efficient and technically simple to carry out.

Keywords: Bradsher cyclization; C−C coupling; acenes; aldehydes; arenes; aromaticity.