Photo‐Induced Homologation of Carbonyl Compounds for Iterative Syntheses

We describe a photo‐induced reaction for the in situ generation of highly reactive alkyl diazo species from carbonyl precursors via photo‐excitation of N‐tosylhydrazone anions. The diazo intermediates undergo efficient C−H insertion of aldehydes, leading to the productive synthesis of aldehydes and ketones. The method is applicable to the iterative synthesis of densely functionalized carbonyl compounds through sequential trapping of the diazo species with various aldehydes. The reaction proceeds without the need of any catalyst by light irradiation and features high functional group tolerance. More than 70 examples, some performed on a gram‐scale, demonstrate the broad applicability of this reaction sequence in synthesis. A photo‐induced Büchner‐Curtius‐Schlotterbeck type reaction for carbonyl homologation is described. The protocol allows the use of carbonyl compounds as safe and readily available diazo precursors through direct photoexcitation of corresponding N‐tosylhydrazone anions. Functionalized aliphatic aldehydes and ketones are prepared in a practical and iterative manner.