Concerted and Stepwise Mechanisms in the Eliminations from 1,2-Dihalogenoacenaphthenes Promoted by Potassium tert-Butoxide and Potassium Ethoxide in the Corresponding Alcohols

Article abstract of DOI:10.1021/jo00138a007

Anti and syn eliminations from cis- and trans-dihalogenoacenaphthenes, respectively, have been investigated in t-BuOK-t-BuOH and EtOK-EtOH.The leaving group ability order for the syn eliminations in t-BuOK-t-BuOH is F > Cl ca.Br, which suggests an (E1cB)_I mechanism.Also consistent with this mechanism is the observation that from trans-1-chloro-2-fluoroacenaphthene only HF is eliminated.In EtOK-EtOH the order of leaving group ability for the syn eliminations is Br > Cl > F, which might suggest an E2 mechanism; however, the leaving group effects are very small, anda stepwise mechanism cannot be excluded.The anti eliminations from the cis-dihalogenoacenaphthenes exhibit a substantial leaving group effect; on this basis and also on considering the β-halogen effect on the rate of elimination, a concerted mechanism is suggested.