Novel Betaines of the Hexaalkylguanidinio-carboxylate Type

Betaines 7a, b and 8a, b have been prepared from 3- and 4-piperidinecarboxylic acid and N,N,N',N'-tetraalkyl-chloroformamidinium chlorides via the corresponding methyl esters. These betaines are highly hygroscopic, thermally very stable, and, with the exception of 7b, have rather low melting points. They undergo a surprisingly facile alkaline cleavage of the hexaalkylguanidinium moiety. They react with dichloromethane by a twofold nucleophilic substitution to form methylene dicarboxylates such as 11. TheNMR (1H, 13C) data of betaines 7 and 8 are discussed