Preparation of New Nitrogen-Bridged Heterocycles. XXVI. Crystal Structures of Thieno(3,2-a)-and Thieno(2,3-b)indolizine Derivatives.

Single crystal X-ray analyses of thieno[3, 2-a]- and thieno[2, 3-b]indolizine derivatives were carried out and their structures were definitively established. The tricyclic ring systems in both molecules were nearly planar and their deviations from the least-squares planes were less than 6.26°. The structural factors for their indolizine moieties were very similar to those for known aromatic indolizines, but those for the thiophene rings were somewhat different. The deviation from co-planarity and the deformation of the thiophene ring in thieno[3, 2-a]indolizine were greater than those in thieno[2, 3-b]indolizine.