A Concise Route to Keto‐Bridged Polyphenols by Photo‐Fries Rearrangement in Flow

Described is a new synthetic route to bis(2‐hydroxy‐3,5‐di‐t‐butylphenyl)methanone and its derivatives. The combined esterification/photo‐Fries rearrangement approach enables a modular preparation of keto‐bridged polyphenols. This protecting group‐free process is highly atom‐ and step‐economic, and a scalable production was easily achieved in the continuous‐flow mode. A novel synthetic route to densely substituted keto‐bridged polyphenols is developed. The strategy takes advantage of a combined esterification/photo‐Fries process, enabling the modular synthesis of bis(2‐hydroxy‐3,5‐di‐t‐butylphenyl)methanone and its derivatives. A greater throughput of the photo‐rearrangement products can be readily achieved by applying a continuous‐flow system.