Transition metal catalysis plays a pivotal role in transforming unreactive C–H bonds. However, regioselective activation of distal aliphatic C–H bonds poses a tremendous challenge, particularly in the absence of directing templates. Activation of a methylene C–H bond in the presence of methyl C–H is underexplored. Here we show activation of a methylene C–H bond in the presence of methyl C–H bonds to form unsaturated bicyclic lactones. The protocol allows the reversal of the general selectivity in aliphatic C–H bond activation. Computational studies suggest that reversible C–H activation is followed by β-hydride elimination to generate the Pd-coordinated cycloalkene that undergoes stereoselective C–O cyclization, and subsequent β-hydride elimination to provide bicyclic unsaturated lactones. The broad generality of this reaction has been highlighted via dehydrogenative lactonization of mid to macro ring containing acids along with the C–H olefination reaction with olefin and allyl alcohol. The method substantially simplifies the synthesis of important bicyclic lactones that are important features of natural products as well as pharmacoactive molecules.

过渡金属催化在转化惰性 C-H 键方面发挥着关键作用。然而，远端脂肪族 C-H 键的区域选择性激活提出了巨大的挑战，特别是在没有定向模板的情况下。甲基 C-H 存在下亚甲基 C-H 键的活化尚未得到充分研究。在这里，我们展示了在甲基 C-H 键存在下亚甲基 C-H 键的活化，形成不饱和双环内酯。该方案允许逆转脂肪族 C-H 键激活的一般选择性。计算研究表明，可逆的C-H活化之后是β-氢化物消除，生成Pd配位的环烯烃，该环烯烃经历立体选择性C-O环化，随后进行β-氢化物消除，得到双环不饱和内酯。通过含中环到大环的酸的脱氢内酯化以及与烯烃和烯丙醇的 C-H 烯化反应，突出了该反应的广泛普遍性。该方法大大简化了重要双环内酯的合成，双环内酯是天然产物以及药用活性分子的重要特征。