Preparation of Dithienylphospholes by 1,1-Carboboration

In this study the scope of the 1,1‐carboboration reaction was extended to the preparation of mixed heterole‐based conjugated π‐systems. Two arylbis(alkynyl)phosphane starting materials 2 were synthesized bearing two thiophene isomers at the alkyne units and the bulky tipp‐substituent (tipp=2,4,6‐triisopropylphenyl) at the phosphorous atom. The bis(thienylethynyl)phosphanes 2 were converted into the corresponding 2,5‐thienyl‐substituted 3‐borylphospholes 4 in a double 1,1‐carboboration reaction sequence employing the strongly electrophilic B(C6F5)3 reagent under mild reaction conditions. Subsequent Suzuki–Miyaura type cross‐coupling yielded the corresponding 3‐phenylphospholes 7 in a one‐pot procedure from phosphanes 2 in high yields. Phospholes 7 were converted into the respective phosphole oxides 8. A photophysical characterization of derivatives 7 and 8 was carried out. The results presented here demonstrate the suitability of the 1,1‐carboboration reaction for the preparation of phosphole‐/thiophene‐based, light‐emitting systems. Pulling a crowd: Highly substituted thiophene–phosphole–thiophene monomers and their P‐oxides are accessible in high overall yields by a one‐pot 1,1‐carboboration/Suzuki–Miyaura‐type cross‐coupling sequence and subsequent H2O2 oxidation (see scheme, tipp=2,4,6‐triisopropylphenyl). The photophysical properties were determined in solution, in the solid state, and in a poly(methyl methacrylate) matrix.