One‐Pot l ‐Proline‐Mediated Stereoselective α‐C(sp 2 )–H Fluorination of α,β‐Unsaturated Aldehydes through Methoxyfluorination–Elimination

A one‐pot, two‐step l ‐proline‐mediated stereoselective α‐C(sp 2 )–H fluorination of α,β‐unsaturated aldehydes towards their corresponding ( Z )‐α‐fluoro‐α,β‐unsaturated aldehydes has been developed. The first step utilises Selectfluor as a fluorinating agent in CH 3 NO 2 /MeOH forming ( Z )‐α‐fluoro‐α,β‐unsaturated aldehydes and their corresponding dimethyl acetals through methoxyfluorination‐elimination. In the second step, water is added to promote the hydrolytic cleavage of the dimethyl acetals. The obtained ( Z )‐α‐fluoro‐α,β‐unsaturated aldehydes were smoothly reduced to the corresponding alcohols by using NaBH 4 .