Generation and amplification of optical activity of axially chiral N-(1-naphthyl)-2(1H)-pyrimidinethione by crystallization

X-Ray crystallographic analysis of N-(1-naphthyl)-2(1H)-pyrimidinethione revealed that the space group was tetragonal and chiral P4₃. The rate of racemization due to the C–N bond rotation was considerably influenced by the solvent properties. A nonpolar solvent lowers the ΔG^‡value by about 3.0 kcal mol⁻¹ relative to the value in a polar or a protic solvent. The crystallization of racemic axially chiral pyrimidinethione at high temperature led to the chiral breaking of symmetry up to 91% ee.