Addition of methylmagnesium iodide/cuprous iodide or of lithium dimethylcuprate to 2-exo- and 2-endo-methyl-1-(phenylsulfonyl) bicyclo [llO] 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, 3- ...