Pd‐catalysed indirect and regioselective phosphonation of azobenzenes: toward the design of water‐soluble photoswitches

An efficient palladium‐catalysed ortho C‐H acyloxylation of azobenzenes, allowing the introduction of the difunctionalised substituent, diethyl phosphonoacetate, is reported. Thanks to the mild reaction conditions implemented, this regioselective late‐stage ortho‐functionalisation tolerates a wide range of functional groups and permits the access of diversely substituted azobenzenes in good to excellent yields. Selective hydrolysis of the diethyl phosphonate group leads to stable water‐soluble azo‐photoswitches with interesting photophysical properties such as an extended Z‐isomer half‐life, opening new opportunities in the design of optochemical tools for the exploration of living organisms.