Abstract
The cocrystalline salt 2-aminopyridinium propynoate (4) was prepared by mixing 2-ami- nopyridine and propynoic acid in acetone. Heating solid 4 at 100 °C for 2 h leads to a 9:10
mixture of 2-imino-l-2H-pyridine-(S)-acrylic acid (5) and 2H-pyrido[ 1,2-a]pyrimid-2-one (6). The reaction is one of two rare examples of such an addition reaction in the solid state and is
highly chemospecific compared to the analogous reaction in solution. Structure-reactivity relationships for 4 as well as the crystal structure of 5 are discussed. Crystal data: 4: monoclinic,
space group P2i/n, a = 11.503(3), b = 7.004(2), c = 11.052(3) A; ß = 110.19(3)°; R = 0.047, Rv = 0.047 for 799 data for which I > 1.96 (7). 5: monoclinic, space group P2i/c, a = 15.458(4),
b = 15.506(4), c = 7.133(2) A; ß = 102.00(3)°; R = > 1.96 (7).