TANDEM ADDITION CYCLOADDITION REACTION OF OXIMES WITH 2,3-BIS(PHENYLSULFONYL)-1,3-BUTADIENE AS A METHOD FOR 4-PIPERIDONE SYNTHESIS

The reaction of oximes with 2,3-bis(phenylsulfonyl)-1,3-butadiene affords 7-oxa-1-azanorbornanes in high yield. The formation of the bicyclic isoxazolidine involves conjugate addition of the oxime onto the diene to give a transient nitrone that then undergoes a subsequent intramolecular dipolar cycloaddition reaction. The coupling of several oximes with divinyl sulfone was also studied, and related cycloadducts were obtained in excellent yield. The stereochemistry of the cycloaddition is best explained in terms of an exclusive reaction of the Z isomer of the nitrone via an easily attainable endo orientation of the reactive groups. Molecular mechanics calculations have been refined to accurately predict the regiochemistry of the intramolecular cycloaddition. Treatment of these 7-oxa-1-azanorbornanes with Raney nickel in methanol results in reductive nitrogen-oxygen bond cleavage to give substituted 4-piperidones. The bicyclic isoxazolidine derived from cyclohexanone oxime and bis(phenyl-sulfonyl)diene was converted to the azaspiro[5.5]undecane ring system, which is representative of the key ring skeleton of the perhydrohistrionicotoxin family of alkaloids.