Department of Chemistry, The University of Texas at San Antonio , San Antonio, Texas 78249, United States.
J Org Chem. 2017 Aug 18;82(16):8506-8513. doi: 10.1021/acs.joc.7b01163. Epub 2017 Aug 4.
Allylic oxidation of heteroatom substituted cyclic alkenes by tert-butyl hydroperoxide (70% TBHP in water) using catalytic dirhodium caprolactamate [Rh(cap)] forms enone products with a variety of 2-substituted cyclic enamides and 3,4-dihyro-2H-pyrans. These reactions occur under mild reaction conditions, are operationally convenient to execute, and are effective for product formation with as low as 0.25 mol% catalyst loading. With heteroatom stabilization of the intermediate allylic free radical two sites for oxidative product formation are possible, and the selectivity of the oxidative process varies with the heteroatom when R = H. Cyclic enamides produce 4-piperidones in good yields when R = alkyl or aryl, but oxidation of 2H-pyrans also gives alkyl cleavage products. Alternative catalysts for TBHP oxidations show comparable selectivities but give lower product yields.
三价铑环戊内酰胺[Rh(cap)]催化叔丁基过氧化氢（水中 70%TBHP）对杂原子取代的环状烯烃进行烯丙基氧化，可形成各种 2-取代环状烯酰胺和 3,4-二氢-2H-吡喃的烯酮产物。这些反应在温和的反应条件下进行，操作方便，催化剂用量低至 0.25mol%时，产物生成效率高。由于中间体烯丙基自由基的杂原子稳定，有两个位置可用于氧化产物的形成，并且当 R = H 时，氧化过程的选择性随杂原子的不同而变化。当 R = 烷基或芳基时，环状烯酰胺可高产率地生成 4-哌啶酮，但 2H-吡喃的氧化也会产生烷基裂解产物。TBHP 氧化的替代催化剂具有可比的选择性，但产率较低。
