The evolution and application of such a synthetic strategy is linked to advances in the fields of photoredox catalysis 5, 6, 7 and electrochemical synthesis 8, 9 and, especially, their combination with first-row transition-metal catalysis 10, 11, 12, 13. Particularly, disconnections based on the coupling of alkyl-radical fragments have been shown to hold tremendous potential in making C( sp 3)–C and C( sp 3)–heteroatom bonds 3, 4. Metal-catalysed radical cross-coupling reactions represent a conceptual paradigm shift from the historical two-electron polar disconnections 1, resulting in a new approach for the synthesis of organic molecules 2. Mechanistic investigations of this reactivity led to the development of a bismuth-catalysed C( sp 3)–N cross-coupling reaction that operates under mild conditions and accommodates synthetically relevant NH-heterocycles as coupling partners. The resulting Bi(III)–C( sp 3) intermediates display divergent reactivity patterns depending on the α-substituents of the alkyl fragment. This reactivity paradigm for bismuth gives rise to well-defined oxidative addition complexes, which could be fully characterized in solution and in the solid state. Here we show how a low-valency bismuth complex is able to undergo one-electron oxidative addition with redox-active alkyl-radical precursors, mimicking the behaviour of first-row transition metals. However, the use of main-group elements to harness this type of reactivity has been little explored. Radical cross-coupling reactions represent a revolutionary tool to make C( sp 3)–C and C( sp 3)–heteroatom bonds by means of transition metals and photoredox or electrochemical approaches.
0 Comments
Leave a Reply. |