Degenerate rearrangement of bicyclo 3.1.0 hex-2-ene

Degenerate rearrangement of bicyclo[3.1.0]hex-2-ene (Chart 2) has a PES, in which four degenerate products are separated through four degenerate TSs with the common energy plateau on the surface.9 Here, four compounds are identical except for the position of deuterium. The rearrangement from 4-exo isomer (6x) is expected to afford 4-endo (6n), 6-exo (7x), and 6-endo (7n) isomers in equal amount if the reaction follows statistical reaction theory (TST). Thus, this reaction provides a situation previously presented by Carpenter to predict nonstatistical product distribution due to dynamics effect.1... 

Houk and co-workers reported a theoretical study of the degenerate rearrangement of bicyclo[3.1.0]hex-2-ene labeled with deuterium in the 4-exo position (113 in Figure 11.113) that offers additional insight into the nonsta-tistical dynamics model of reactivity. Breaking the Cl—C5 bond of 113 leads to a diradical (114) that can reclose to 113 with retention of configuration at both Cl and C5 (the rr path), can close suprafacially to 115 with retention at C5 (the rs path), can close to 116 with inversion at both Cl and C5 (the ii path), or can close antarafacially to 117 with inversion at C5 (the ia path). Baldwin and Keliher had reported that the activation parameters for formation of 115, 116, and 117 are identical and that the ratio of relative rate constants k s ku ki is 48 36 16. ... 

---