Metal-free acceptorless dehydrogenative cross-coupling of aldehydes/alcohols with alcohols†
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Abstract
Although transition metal catalyzed dehydrogenative cross-coupling reactions have achieved great success for accessing carbon–carbon and carbon–heteroatom bonds during the past decade, metal-free acceptorless dehydrogenative cross coupling is still scarce and highly desirable. Herein we report a robust metal-free acceptorless dehydrogenative cross-coupling for both carbon–heteroatom and carbon–carbon bond formation. By synergistic catalysis of the organophotocatalyst 4CzIPN and a thiol under blue light irradiation, the cross-coupling of aldehydes with alcohols or of two different alcohols proceeds smoothly with a broad substrate scope and good functional group compatibility, providing the corresponding esters in satisfactory yields along with the release of hydrogen gas. A dehydrogenative intramolecular acylation leading to fluorenone derivatives is also realized by this metal-free redox-neutral process. Mechanistic studies indicate the generation and subsequent oxidation of an acyl radical to its cation under photocatalytic conditions.
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