Ring-Closure Reactions. 22. Kinetics of Cyclization of Diethyl (ο-Bromoalkyl)malonates in the Range of 4- to 21-Membered Rings. Role of Ring Strain

Article abstract of DOI:10.1021/ja00316a039

The kinetics of closure of 1,1-bis(ethoxycarbonyl)cycloalkanes from the anions derived from diethyl (ο-bromoalkyl)malonates have been investigated in Me2SO at 25 degC.Rate constants and effective molarities (EM) have been obtained for the ring sizes 4-13, 17, and 21.This is the first quantitative study on the kinetics of S_N2 closure of all-carbon rings, which includes small, common, medium and large rings.The reactivity data span over nine powers of ten, which is the widest reactivity range recorded so far in a cyclization series.Due to the extremely low EM for the 9-, 10-, and 11-membered rings, a special competition technique was developed for these rings.Comparison of the present results with literaturee data on S_N2 ring-closure reactions reveals structure-dependent reactivity patterns showing varying features, which are qualitatively accounted for on the basis of structure effects on transition-state strain energies.A dissection of the EM data for the malonate cyclization into strain and probability factors was attempted.Perhaps the most interesting result is a definite tendency for transition-state strain energies to parallel cycloalkane strain energies for the 7-membered and larger rings but not for the smaller rings.In the latter cases the ring product no longer appears to be a proper model for comprehending the transition state.