Regio- and Stereoselective Synthesis of Enynyl Boronates via Ruthenium-Catalyzed Hydroboration of 1,4-Diaryl-Substituted 1,3-Diynes

Authors:

• Tomasz Sokolnicki,
• Jakub Szyling,
• Adrian Franczyk,
• Jędrzej Walkowiak

Abstract

Abstract A facile ruthenium-catalyzed regio- and stereoselective hydroboration of symmetrical, aromatic 1,3-diynes with pinacolborane towards 2-boryl-1,4-diaryl-buta-1-en-3-ynes and their further transformation into potassium trifluoroborate salts is presented. The reaction proceeded efficiently for 1,4-diphenylbutadiynes with various substituents on the phenyl rings and heterocyclic 1,4-di(thiophen-3-yl)buta-1,3-diyne. The resulting products were isolated and fully characterized (1H, 13C, 11B and 1D NOESY NMR, IR, GC-MS, HRMS or elemental analysis). Moreover, the crystal structure of an enynyl boronate was determined, proving the addition of boryl moiety at the internal carbon in the diyne, according to the anti-Markovnikov rule. The results presented here are the first examples of selective catalytic monohydroboration of conjugated diynes. The products obtained due to the presence of the boryl group and the unsaturated bonds are potential synthons in the synthesis of natural compounds or active pharmaceutical ingredients (API). The model Suzuki coupling of 2-boryl-1,4-diphenyl-buta-1-en-3-ynes with iodobenzene was carried out to illustrate the utility of the resulting compounds.