Mercuric Acetate Cyclization of 4-(Pyrrolylmethyl)- and 4-(Indolylmethyl)piperidines to Bridged Polycyclic Systems

Article abstract of DOI:10.1021/jo00173a010

The mercuric acetate cyclization of 4-(pyrrolylmethyl)piperidines 4 and 9 as well as of 4-(indolylmethyl)piperidines 13 and 18 to the corresponding bridged polycyclic systems is studied.When the reaction was carried out in aqueous AcOH solution, mixtures of the starting piperidine and the corresponding cyclized product were obtained.The recovery of piperidine is attributed to the mercuration of the heteroatomic ring, which prevents the cyclization of the intermediate iminium salt.In the pyrrole series, the use of EDTA in alkaline medium avoids mercuration and gives rise exclusively to the cyclized products 5 and 10 in high yields.However, these alkaline conditions are not appropriate for cyclization of (indolylmethyl)piperidines, because of the formation of the corresponding 2-piperidinones 15 and 20 as the major products.The best yield of methanoazociniondole 14 was obtaind when the oxidative cyclization of 13 was effected in the presence of EDTA at pH 6-7, whereas methanodiazocinoindole 19 was more conveniently prepared in aqueous EDTA solution.