Stereoselectivity in a series of 7‐alkylbicyclo[3.2.0]hept‐2‐enes: Experimental and computational perspectives

Rate constants for overall decomposition ( k d ) for a series of exo ‐7‐alkylbicyclo[3.2.0]hept‐2‐enes are relatively invariant. For the alkyl substituents ethyl, propyl, butyl, isopropyl, and t ‐butyl, the ratio of the rate constant for [1,3] sigmatropic rearrangement to the rate constant for fragmentation, k 13 / k f , is significantly lower than k 13 / k f  = 150 observed for exo ‐7‐methylbicyclo[3.2.0]hept‐2‐ene. Regardless of the size and mass of the alkyl group, the stereoselectivity of the [1,3] carbon migration appears to be quite stable at 80% to 89% suprafacial inversion ( si ), an observation consistent with conservation of angular momentum but not conservation of orbital symmetry. This global result comports with the phenomenon of “dynamic matching” espoused by Carpenter and collaborators for [1,3] sigmatropic rearrangements in general.