Synthesis of retinals labelled with 13C in the cyclohexene ring

In this paper we report the synthesis of five retinals, specifically mono‐labelled with 13C at the positions 1, 2, 3 and 4 and di‐labelled with 13C at the positions 16 and 17, with more than 98% chemical purity and high 13C incorporation. (1‐13C)‐ and (16, 17‐13C2)retinal were obtained in 20% overall yield from (2‐13C)‐ and (1,3‐13C2)acetone. (2‐13C)‐ and (3‐13C)retinal were prepared in 10% overall yield from (1‐13C)‐ and (2‐13C)acetonitrile, while (4‐13C)retinal was synthesized in 17% overall yield starting from (2‐13C)acetonitrile.