In the title compound, C 14 H 11 ClN 2 O 2 S, the dihedral angle between the pyrrolo[1,2-c]pyrimidine ring system (r.m.s. deviation = 0.008 Å ) and the benzene ring is 80.2 (9) . In the crystal, inversion dimers linked by pairs of C-HÁ Á ÁO interactions generate R 2 2 (16) loops. Several aromaticstacking interactions between the pyrrolo[1,2-c]pyrimidine rings, as well as separately between the pyrrolo and pyrimidine groups [shortest centroid-centroid separation = 3.5758 (14) Å ], help to consolidate the packing.

The synthesis of several new pyrrolo [1,2-c]pyrimidines from the base-induced condensation of pyrrolo-2-carbaldehydes with either TosMIC (toluenesulfonylmethyl isocyanide) or ethyl isocyanoacetate is described, along with the preparation of novel bis(pyrrolo[1,2-c]pyrimidines).The pyrrolo[1,2-c]pyrimidine ring system has an interesting history. In 1949 Herz inadvertently synthesized 1-phenylpyrrolo[1,2-c]pyrimidine-3-carboxylic acid (1), the first example of this ring system, in a reinvestigation of the reaction between pyrrole-2-carbaldehyde and hippuric acid. 1 In 1963 Boekelheide achieved the first targeted synthesis of this ring system with the preparation of 3-methyl-6-phenylpyrrolo[1,2-c]pyrimidine (2) via a classical Chichibabin reaction. 2 The parent molecule 3, which was found to be aromatic though oxidatively labile, was prepared by Rapoport in 1965 via the cyclization of 3-(4-pyrimidyl)-1-propanol (or its tosylate) and subsequent dehydrogenation. 3 Rapoport also isolated 3-methyl-6,7-dihydro-5H-pyrrolo[1,2-c]pyrimidin-1-one (4) as a chemical degradation product of the toxic shellfish poison, saxitoxin. 4 More recently, variants of Boekelheide's Chichibabin approach to pyrrolo[1,2-c]pyrimidine 2 have been implemented in syntheses of this ring system, 5 and the synthesis of all of the isomeric pyrrolopyrimidines has been reviewed. 6