Guanidines easily react with not only acidic compounds but also electrophiles such as alkyl halides, to form the corresponding stable salts due to effective resonance. Thus, modified guanidines could be expected to play important roles as chiral auxiliaries in asymmetric synthesis if chiral environment is produced in reactive salt intermediates. This article reviews the preparation of modified guanidines and their application to asymmetric synthesis. Reasonable asymmetric inductions were

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... d not only in catalytic but also in stoichiometric asymmetric syntheses. These guanidine-mediated reactions may contribute to development of green chemistry because of their possible uses as recyclable (economically favored) and easily functionalizable (widely applicable) auxiliaries.