Guanidines: powerful bases for organic synthesis

Guanidines are a type of organic compounds that have gained increasing importance in organic synthesis processes over time. The functional group that characterises them consists of a carbon atom bonded to three nitrogen atoms and is present in some biologically relevant molecules such as arginine (an essential amino acid) or creatine.

They are related to other nitrogen-containing functionalities such as amines, amidines, imines, or ureas, and are characterized by their strongly basic nature. Some of them have been referred to as “superbases” for being stronger bases than the hydroxide ion, the strongest base in aqueous solution.

Their interest lies not only in their strength as bases but also in their lack of nucleophilic character. Some amidine-type bases such as DBN (1,5-diazabicyclo-[4.3.0]non-5-ene) or DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) are widely used in synthesis, but they are not economical and easily rented. This problem is avoided by using amidines, which are strong non-nucleophilic bases, or by using sterically hindered guanidines.

Preparation and characteristics