Hydride Transfer-Initiated Cross-Dehydrogenative Coupling Reaction to Access Nine-Membered Rings.

An unprecedented hydride transfer-triggered cross-dehydrogenative coupling of two C(sp3)-H bonds to target nine-membered rings has been developed. Salient features of this methodology include atom and step economy and metal-free and redox-neutral conditions, with water as the byproduct and proceeding well even with decomposed aldehydes.