A Click‐Type Reaction of ( <i>RRR</i> )‐α‐Tocopherol and Related 6‐Chromanols Allowing a One Pot Derivatisation of All Fat‐Soluble Vitamins

(RRR)-α-tocopherol reacts with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) at ambient conditions in a fast formal [6+2+2] addition reaction yielding four pairs of diastereomers, three of them containing novel heterocyclic ring systems. Structure elucidation required customized 3,5-¹³C₂,4-¹⁵N labelled PTAD to establish the connectivity of the PTAD units using ^4-5J ¹H-¹³C, ²J ¹³C-¹³C, and ¹J ¹³C-¹⁴N NMR correlations. Absolute stereochemistry was determined based on calculated CD spectra compared to experimental data. The reaction occurred also with related 6-chromanols and required a free phenolic hydroxy group. As one possibility, the addition of the first PTAD involves a hetero-Alder-ene reaction, followed by a Diels-Alder or alternative addition / cyclization of a second PTAD. Together with the derivatization of vitamin K and the known reactions with vitamins A and D, PTAD can thus derivatize all fat-soluble vitamins in a one pot reaction, offering potential new applications for their analysis in complex matrices.