Reversible Umlagerung eines cis‐2‐Vinyl‐cyclopropylformaldehydes zu einem Dihydrooxepin. Vorläufige Mitteilung

Evidence is given for a fast reversible 2‐vinylcyclopropylformaldehyde‐dihydro‐oxepine rearrangement. Bicyclo[3.1.0]hex‐2‐ene‐6‐endo‐formaldehyde and 2‐oxa‐bicylo[3.2.1]octa‐3,6‐diene coexist in a 7:3 equilibrium, which is pulled in the direction of the enol ether by a cycloaddition with tetracyanoethylene, and in the direction of the aldehyde by interaction with LiAlH 4 , Ag 2 O or NaHSO 3 . Decomposition of the pure hydrogensulfite adduct of the aldehyde refurnishes the 7:3 mixture.