Key indicatorsSingle-crystal X-ray study T = 100 K Mean '(C±C) = 0.003 A Ê R factor = 0.049 wR factor = 0.128 Data-to-parameter ratio = 12.6For details of how these key indicators were automatically derived from the article, see

Key indicatorsSingle-crystal X-ray study T = 100 K Mean '(C±C) = 0.003 A Ê R factor = 0.072 wR factor = 0.155 Data-to-parameter ratio = 12.5For details of how these key indicators were automatically derived from the article, see

Key indicatorsSingle-crystal X-ray study T = 173 K Mean (C-C) = 0.005 Å R factor = 0.067 wR factor = 0.177 Data-to-parameter ratio = 20.9For details of how these key indicators were automatically derived from the article, see

The reaction between 4‐dimethylaminopyridine (DMAP) and 2‐bromoacetophenone(s) readily gives 1‐ [2‐(4‐substitutedphenyl)‐2‐oxoethyl]‐4‐(dimethylamino)pyridinium bromide (1–14). Action of aqueous NaOH on 1–8 generates the corresponding pyridinium ylide (15–22), which is isolated as a colored stable crystalline solid. Addition of 15–22 to dimethylacetylene dicarboxylate (DMAD) gives dimethyl 3‐(substitutedbenzoyl)‐7‐(dimethylamino)indolizine‐1,2‐dicarboxylate (23–30) in 46–62% yield.

In both of the title compounds, C(23)H(19)ClN(2)O, (I), and C(23)H(18)Cl(2)N(2)O, (II), the molecular packing is influenced by weak intermolecular C-H.O and C-H.pi interactions, but despite the chemical similarity of the compounds, the packing in (II) is entirely different from that observed in (I).