Metal-free acceptorless dehydrogenative cross-coupling of aldehydes/alcohols with alcohols

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.