EVIDENCE OF REVERSIBLE ZWITTERION FORMATION IN REACTION OF 7-KETONORBORNANE AND DIMETHYLOXOSULFONIUM METHYLIDE

Dimethyloxosulfonium methylide reacts with excess 7-ketonorbornane in dimethyl sulfoxide at room temperature to produce a complex mixture containing spiro [norbornan-7,2′-oxacyclopropane], methyl 7-(7-hydroxynorbornyl) carbinyl sulfoxide, bis[7-(7-hydroxynorbornyl)carbinyl] sulfoxide and no unreacted ketone. We attribute this unusual and heretofore unobserved reaction type to steric crowding by the exo-2,3 hydrogens of the ketone which forces the betaine-type intermediate to adopt a conformation from which hydride transfer rather than intramolecular displacement is the dominant reaction. When the reaction is stopped prior to completion, a metastable intermediate can be isolated which reacts with 7-ketonorbornene to produce spiro [norborn-2-en-anti-7,2′-oxacyclopropane] in addition to the other products. It is suggested that this reversibly formed insoluble intermediate is the betaine-type zwitterion derived from the addition of bis [7-(7-hydroxynorbornyl)-carbinyl] oxosulfonium methylide to 7-ketonorbornane. © 1969, American Chemical Society. All rights reserved.