Microwave-assisted synthesis of highly functionalized guanidines on soluble polymer support

An efficient method for the N,N′-di(Boc)-protected guanidines containing piperazine and homopiperazine scaffolds has been developed under multi-step microwave irradiation. Followed by alkylation of carbamate-protected guanidines with various alkyl halides is also explored. This protocol proceeds via deprotonation of the acidic N-carbamate hydrogen of the guanidine by sodium hydride on soluble polymer support. In this manner, highly functionalized guanidines were obtained after cleavage from the support. The reaction is tolerant of a wide range of functional groups on both the alkyl halide and guanidine components. In addition, the reaction is sufficiently simple workup by precipitation in each step to yield the substituted guanidines in high purity. In conjunction with microwave irradiation and soluble polymer support, this method provides an efficient route to access highly functionalized guanidines.