Short, Convergent Synthesis of Locked Retinals

We report a short and convenient synthesis of two configurationally locked retinals that are important for applications in the context of optogenetics. The C11–C15 cyclopentyl fragments of both retinals were obtained by palladium‐catalysed alkoxycarbonylation and merged with the rest of the carbon skeleton through Wittig olefination. The preparation of the required and known ylide precursor was revisited and optimised. This synthetic route enables gram‐scale preparation of both retinal derivatives. A short synthesis of two configurationally locked retinals is reported, that relies on alkoxycarbonylation and Wittig olefination as key steps. The convergent reaction sequence differs from previous syntheses of comparable locked retinoids by a common preparative approach of the two carbonyl precursors for the Wittig olefination and by a useful total yield of both retinals.