Development of a Scalable Route for a Highly Polar Heterocyclic Aminocyclopropyl Building Block

A robust and scalable route toward key heterocyclic building block 1-(pyrimidin-2-yl)cyclopropan-1-amine hydrochloride from cyclopropanated starting material 1-amino-1-cyclopropanecarbonitrile hydrochloride was successfully developed. The key to success was the construction of a pyrimidine ring via cyclization from an amidine intermediate and a bench-stable 2-chloro vinamidinium hexafluorophosphate salt. The cyclization was performed under mild conditions, and the resulting 4-cloropyrimidine derivative was isolated in high yield and purity. The final hydrogenation was intensively optimized: A combination of Pd(OH)₂/C as a catalyst and NaOMe as a base at 1 bar H₂ pressure in MeOH simultaneously cleaved the Cbz group and dechlorinated the pyrimidine ring while at the same time suppressing the over-reduction of the pyrimidine ring to below 1.0%. After acidification with HCl, followed by removal of the catalyst and NaCl by filtration, the final product was isolated in high yield and purity as a bench-stable off-white solid. The overall yield of the five-step sequence was 57%.