Sterically Controlled Population of the 1,2-cis-Form of 1,2-Dimethyl-3-tert-butyldiaziridine.

1,2-Dimethyl-3-R-diaziridine (R = But) has been synthesized for the first time; as revealed by NMR the population of its 1,2-cis-form was shown to increase in polar solvents [1,2-cis/1,2-trans = 2 (D2O), 0.5 (CDCl3), 0.03 (C6D6); for 1,2-trans → 1,2-cis in C6D6 at 32 °C ΔG# = 25 kcal mol-1] whereas solely the 1,2-trans-form was detected in diaziridines when R = Me, Et, Pri, Ph.