Modified guanidines could effectively mediate asymmetric silylation of secondary alcohols as recyclable bases under simple and mild conditions.

Modified guanidines were explored as potential chiral superbases. Thus, chiral 1,3-dimethyl-2-iminoimidazolidines with or without 4, 5-diphenyl groups, their guanidinium salts, and the 2-iminoimidazolidines with (S)-1-phenylethyl groups on the ring nitrogens were prepared by treatment of 2-chloroimidazolinium chlorides with appropriate amines. Bicyclic guanidines were also prepared from a prolinamide using a similar procedure.

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