Diastereoselective Hydrogen-Transfer Reactions: An Experimental and DFT Study

作者：Godin Francois; Prevost Michel; Gorelsky Serge I; Mochirian Philippe; Maud Nguyen; Viens Frederick; Guindon Yvan^*

来源：Chemistry - A European Journal, 2013, 19(28): 9308-9318.

DOI：10.1002/chem.201300377

• borinate
• conformational analysis
• density-functional calculations
• diastereoselectivity
• radical reactions

Radical reductions of halogenated precursors bearing a heterocycle exo () to the carbon-centered radical proceed with enhanced anti-selectivity, a phenomenon that we termed exocyclic effect. New experimental data and DFT calculations at the BHandHLYP/TZVP level demonstrate that the origin of the exocyclic effect is linked to the strain energy required for a radical intermediate to reach its reactive conformation at the transition state (Estrain). Furthermore, radical reductions of constrained THP systems indicate that high 2,3-anti inductions are reached only when the radical chain occupies an equatorial orientation. Hydride deliveries to different acyclic substrates and calculations also suggest that the higher anti-selectivities obtained with borinate intermediates are not related to the formation of a complex mimicking an exocycle. From a broader standpoint, this study reveals important conformational factors for reactions taking place at a center vicinal to a heterocycle or an -alkoxy group.

• 出版日期2013-7-8