Modified guanidines as potential chiral superbases. 3. Preparation of 1,4,6-triazabicyclooctene systems and l,4-disubstituted 2-iminoimidazolidines by the 2-chloro-1,3-dimethylimidazolinium chloride-induced cyclization of guanidines with a hydroxyethyl substituent

Simple preparation methods of modified guanidines have been explored as pot ential chiral superbases. Thus, 3,7,8-trisubstituted and 3,6,7,8-tetrasubst ituted 1,4,6-triazabicyclooctene systems were prepared from (1S,2S)-1,2-dip henylethylenediamine through stepwise 2-chloro-1,3-dimethylimidazolinium ch loride (DMC)-induced cyclizations of protected thioureas to the correspondi ng 2-iminoimidazolidines and then of 2-(2-hydroxyethylimino)imidazolidines to the bicyclic systems. Linear guanidines with a 2-hydroxyethyl functional group were prepared by the reaction of carbodiimides with 2-amino alcohols . Reaction of linear-type guanidines with DMC followed by base treatment af forded 1,4-disubstitued 2-iminoimidazolidines. Furthermore, another type of 1,4,6-triazabicyclooctene was also prepared through double DMC-induced cyc lization of guanidines with two a-hydroxyethyl substituents.