Recent development of synthetic preparation methods for guanidines via transition metal catalysis.

Multisubstituted guanidines have received much attention because of important applications in many fields, such as pharmaceutics, organometallic and coordination chemistry, and organic synthesis. Although classical methods are available for the preparation of guanidines, synthetic preparation approaches to guanidines are still in great demand. In this review, we summarize recent developments on synthetic methods via the C-N bond formation. Three aspects are included: transition-metal-catalyzed guanidine synthesis based on classical methods; catalytic guanylation reaction of amines with carbodiimides; and tandem catalytic guanylation/cyclization reactions.