Synthesis of diverse classes of thiahelicenes by transition metal-catalysed cross coupling reactions

Abstract

Tetrathia[7]helicenes (7-THs) are an attractive class of polyconjugated ortho-fused heteroaromatic compounds, endowed with inherent chirality due to the helical shape of their \u3c0-conjugated system.1 Their unique structural and chiroptical properties have stimulated manifold studies in optoelectronics,2 catalysis,3 and biology.4 In our ongoing studies on the synthesis and functionalization of 7-TH systems, we have recently developed an innovative diversity-oriented synthesis of 7-THs exploiting transition metal-catalysed cross coupling reactions as key steps (Figure 1).In this communication we report the synthesis of novel classes of thiahelicenes 1a\uf02dc starting from the key intermediates 2, from which we can obtain: i) helicenes 1a through Sonogashira coupling with terminal alkynes, followed by In- or Pt-catalysed intramolecular hydroarylation of alkynes 3; ii) helicenes 1b through palladium-catalysed annulation of 2 with internal alkynes; iii) helicenes 1c through Suzuki coupling with (hetero)aryl boronic esters, followed by oxidative photochemical cyclization of intermediates 4