Addition of methylmagnesium iodide/cuprous iodide or of lithium dimethylcuprate to 2-exo-and 2-endomethyl-1 -(phenylsulfonyl)bicyclo[ 1.1.0]butane and determination of the relative geometry of the methyls in the 2,3-dimethylcyclobutanes obtained allowed us to establish that addition of the methyl group occurred from the endo side of the bicyclic molecule. Similarly, lithium aluminum hydride reduction of 2-exo,3-and 2-endo,3dimethylbicyclobutane was also found to occur by endo-addition of the hydride ion at position 3 of the bicyclic system.

Methylierungsreaktionen an den Bicyclobutan‐sulfonen (I) werden untersucht, deren Herstellung z.Tl. in der angegebenen Weise beschrieben wird.