The preparation of amino derivatives of p-deficient heterocycles may be achieved by Buchwalde-Hartwig coupling reactions, but they require the use of expensive transition metal catalysts and phosphine ligands and, importantly from the point of view of green chemistry, they cannot be performed in solvent-free conditions.The most common approach involves an additioneelimination reaction between the suitable halogenated heterocycle and amine, which requires very harsh and unsafe conditions, such as heating at high temperatures in sealed tubes or using large amounts of
phenol as the reaction medium. Also importantly from the point of view of waste generation, the conventional conditions often involve the use of a large excess of toxic reagents, such as amines. Furthermore, these methods normally give poor yields, typically below 40-50%, and lead to complex reaction mixtures requiring the use of chromatographic purification. A few attempts have been made recently to solve these problems by application of microwave technology, but the solutions found so far are far from being general. A library of 4-arylaminoquinolines (with two additional examples involving the reaction of aliphatic amines) has been prepared from the corresponding 4-chloroquinolines. However,the conditions described involve the use of a domestic oven, which is associated to safety concerns and serious reproducibility problems owing to the existence of an uneven pattern of hot and cold spots inside the oven cavity. Focused microwave conditions have also been reported for the specific case of the amination of 4-chloroquinolines, but they have the disadvantage of requiring the use of an organic solvent, namely DMSO, and hence of needing extraction and chromatographic purification steps that involve the generation of waste from organic solvents and chromatographic stationary phases.13 These are the main source of waste from academic and industrial laboratories and plants devoted to synthesis and, therefore, the development of solvent-free synthetic methods is of considerable current interest. In this context, it must be borne in mind that it is not the reaction itself, but the extraction and chromatographic purification steps, which have been described as ‘the Medicinal Chemistry bottleneck’, that normally lead to the use of the largest amount of solvents.