Dehydrogenative transformations of alkyl chains to alkenes through methylene C–H activation remain a substantial challenge. We report two classes of pyridine-pyridone ligands that enable divergent dehydrogenation reactions through Pd-catalyzed β-methylene C–H activation of carboxylic acids, leading to the direct syntheses of α,β-unsaturated carboxylic acids or γ-alkylidene butenolides. The directed nature of this pair of reactions allows chemoselective dehydrogenation of carboxylic acids in the presence of other enolizable functionalities such as ketones, providing chemoselectivity that is inaccessible with existing carbonyl desaturation protocols. Product inhibition is overcome through ligand-promoted preferential activation of C(sp³)–H bonds over C(sp²)–H bonds or a tandem dehydrogenation or vinyl C–H alkynylation sequence. The dehydrogenation reaction is compatible with molecular oxygen as the terminal oxidant.

中文翻译：

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通过 C-H 活化进行配体控制的羧酸发散脱氢反应

通过亚甲基 C-H 活化将烷基链脱氢转化为烯烃仍然是一个重大挑战。我们报道了两类吡啶-吡啶酮配体，它们通过钯催化的β-亚甲基C-H活化羧酸实现不同的脱氢反应，从而直接合成α,β-不饱和羧酸或γ-亚烷基丁烯内酯。这对反应的定向性质允许在其他烯醇化官能团（例如酮）存在下对羧酸进行化学选择性脱氢，从而提供现有羰基去饱和方案无法实现的化学选择性。^{通过配体促进的 C(sp 3} )–H 键相对于 C(sp ² )–H 键的优先激活或串联脱氢或乙烯基 C–H 炔基化序列来克服产物抑制。脱氢反应与分子氧作为末端氧化剂相容。