Reactions of 1-halocycloheptenes with potassium t-Butoxide and with sodium pyrrolidide

Reactions of 1-halocycloheptenes with KO-t-Bu in DMSO and THF were studied. The principal products obtained could be accounted for on the basis of two competing dehydrohalogenation mechanisms. These are: dehydrohalogenation across the C₁-C₂ bond to give cycloheptyne; and dehydrohalogenation across the C₁-C₇ bond to give 1,2-cycloheptadiene. One or both of these intermediates react with KO-t-Bu to give 1-t-butoxycycloheptene in poor yield. The principal product from the three 1-halocycloheptenes in both solvents is tricyclo7.5.0.0²8]tetradeca-2,14-diene (4), the dimer of 1,2-cycloheptadiene. Also formed are 5, the 2(8), 14-diene isomer of 4, presumably by cycloaddition of 1,2-cycloheptadiene and cycloheptyne, and 6, the 2,13-diene isomer of 4, by rearrangement of 4 effected by KO-t-Bu.Also studied were rections of 1 chloro- and 1-iodocycloheptene with sodium pyrrolidide (Na- NC₄H₈) in THF. These reactions give 1-(1-pyrrolidino)cycloheptene in fair yield together with smaller amounts of the 14-carbon hydrocarbons. Reactions of 1-chlorocycloheptene-1-¹⁴C and 4-chloro- and 4-iodobicyclo5.1.0]oct-3-ene leading to (1-pyrrolidino)cycloheptenes were found to occur via both the corresponding cycloheptyne and 1,2-cycloheptadiene.