Isomorphous diethyl 1-(4-chloro­benz­yl)-4-(4-chloro­phen­yl)-2,2-dioxo-3,4,6,7,8,8a-hexa­hydro-1H-pyrrolo­[2,1-c][1,4]thia­zine-1,3-di­carboxyl­ate and its 1-(4-methyl­benz­yl)-4-(4-methyl­phen­yl)-substituted analogue obeying the chloro–methyl exchange rule

Accurate studies on the effect of substituents on the crystal packing are essential for understanding the inter­molecular inter­actions and thus paving the way to crystal structure prediction. The crystal structures of diethyl 1-(4-chloro­benz­yl)-4-(4-chloro­phen­yl)-2,2-dioxo-3,4,6,7,8,8a-hexa­hydro-1H-pyrrolo­[2,1-c][1,4]thiazine-1,3-di­carboxyl­ate, C(26)H(29)Cl(2)NO(6)S, (I), and its isomorphous pair diethyl 1-(4-methyl­benz­yl)-4-(4-methyl­phen­yl)-2,2-dioxo-3,4,6,7,8,8a-hexa­hydro-1H-pyrrolo­[2,1-c][1,4]thia­zine-1,3-di­carboxyl­ate, C(28)H(35)NO(6)S, (II), are described. The mol­ecular aggregation patterns appear to be strikingly similar despite changes in the substituents, with a Cl atom in (I) being replaced by a methyl group in (II). Inspite of the chemical modifications, the structures of (I) and (I) are isomorphous, isostructural and found to obey the chlorine–methyl exchange rule. Both the structures feature C—H⋯O hydrogen bonding. However, a distinguishing feature between (I) and (II) is observed in the conformation of the pyrrole rings where the twist occurs on different C—N bonds. Hirshfeld analysis of both structures is presented and discussed.