Steric control in the thermal rearrangement of a bicyclo[3.1.0]hex-2-ene substituted at a radical-nonstabilizing position.

Introduction into the long-known bicyclo[3.1.0]hex-2-ene system of a large substituent in an electronically inactive, interconnected pair of positions brings to light the importance of sterics as a major factor in the determination of products. Far from the "flat" surface that so well describes the caldera of diradicals of the archetype, a "bumpy" surface is required as the conceptual scheme. The relief of "compressional" strain serves to explain the dramatic effect on kinetics and composition at equilibrium.