The reactivity of pseudoaromatic compounds. Part III. Reactions of 2-lodo-, 2-bromo-, and 2-choloro-tropone with quinuclidine

Abstract

Quinuclidine reacts with 2-iodotropone in benzene to give 1-{2-[N-(7-oxocyclohepta-1,3,5-trien-1-yl)piperidin-4-yl]ethyl}-(II) or 1-(7-oxocyclohepta-1,3,5-trien-1-yl)-1-azoniabicyclo[2,2,2]octane iodide (III), or a mixture of both according to the conditions. Experiments with 2-iodo[3,5,7-²H₃]tropone show that the quinuclidine nitrogen atom attacks the 2-position to give compound (III) which kinetic experiments on solutions in dimethyl sulphoxides show to be an intermediate in the formation of (II). The iodide (III) readily rearranges to 2-[4-(2-iodoethyl)piperidino]cyclohepta-2,4,6-trien-1-one (IV). The reaction of 2-chlorotropone with quinuclidine in benzene gives a mixture of the chloride analogues of (II) and (III), whereas in dimethyl sulphoxide, as with 2-bromotropone, only a compound of type (II) is formed with kinetics similar to those for 2-iodotropone. The reaction of 1-chloro-2,4-dinitrobenzene with quinuclidine in benzene fails to give quaternary salts of type (III); only 1-{2-[N-(2,4-dinitrophenyl)piperidin-4-yl]ethyl}-1-azoniabicyclo[2,2,2]octane chloride is obtained, in low yield.