Preparation of deuterium‐labelled retinals having high deuterium content on specific positions 10‐Mono‐, 11‐mono‐, 10,11‐di‐ and 14,20,20,20‐tetradeuterioretinal

Abstract 10‐Mono‐, 11‐mono‐ and 10,11‐dideuterioretinal (in the all‐trans, 9‐cis, 11‐cis and 13‐cis forms) of > 98% purity and the required (> 96%) deuterium incorporation were prepared via LiAlH 4 or LiAlD 4 reduction of the retinylidene derivative 8. Compound 8 was prepared by coupling β‐ionone with 6,6‐dimethoxy‐4‐methyl‐3‐hexen‐1‐yne (6), which had been obtained in high yield from 2‐propynyl bromide and commercial 4,4‐dimethoxy‐2‐butanone (4). Exchange of 4 with D 2 O and base gave 4,4‐dimethoxy‐1,1,1,3,3‐pentadeuterio‐2‐butanone (4a), which in turn, using the same synthetic method, finally provided 14,20,20,20‐tetradeuterioretinal.