ADDITION REACTION OF 4-METHYLENE-4<i>H</i>-HOMOCHROMENE DERIVATIVES WITH TETRACYANOETHYLENE. POSSIBLE INTERVENTION OF A BENZOHOMOPYRYLIUM ION INTERMEDIATE
synthesized with one-pot procedure from α,β-unsaturated thione (chromothione) derivatives by dimethyloxosulfonium methylide. Extremely facile addition of tetracyanoethylene with 4-methylene-4H-homochromenes gave dihydrobenzoxazepine derivatives. The reaction may be well interpreted with the homoaromatic stabilization of the cationic part in a zwitterionic intermediate which would be formed at the rate-determining
The reactions of the methylenehomochromene (titled compound) (1) with orthoformates (2a,b) or acetals (2c–f) easily took place in the presence of anhydrous zinc chloride to give 5-alkoxyethyl-2, 3-dihydro-l-benzooxepin derivatives (3a–f) in moderate to good yields. Unusually high reactivity of 1, may be due to homoaromatic stabilization in the reaction intermediate.