Reactions of lithium salts of O‐alkyl oximes with halogens: A highly stereoselective oxidative coupling of 5,6‐dihydro‐3‐methyl‐4H‐1,2‐oxazine

Lithiation of 5,6‐dihydro‐3‐methyl‐4H‐1,2‐oxazine (4) in an unpolar solvent system (hexane/THF) at −65°C followed by reaction with Cl₂,Br₂, or I₂ affords cleanly and stereoselectively 6 (RS,RS) of which an X‐ray structure analysis is described. In contrast, attempts to couple the halogenated 1,2‐oxazine derivative 5c have given, under various reaction conditions, equal amouts of 6 and 8 (meso). A mechanism of this reaction is discussed.