Synthesis of 6-arylpyrimido[4,5-e]indolizine-2,4(1H,3H)-diones through InCl3-catalyzed cycloisomerization

Abstract

We report the synthesis of hitherto unknown pyrimido[4,5-e]indolizine-2,4(1H,3H)-diones (indolizinouracils) and related polycondensed uracils. The synthetic strategy is based on a chemoselective C–N coupling through an addition–elimination reaction of N,N-dimethyl-5-bromo-6-chlorouracil with N-heterocycles, followed by Sonogashira cross-coupling reaction with alkynes and InCl₃-catalysed cycloisomerisation. The methodology allows for the employment of pyrrole and indole as N-heterocyclic building blocks and tolerates various functional groups. The impact of the substitution pattern on the photophysical properties was studied by steady-state UV-Vis and fluorescence spectroscopy, providing new insights into the potential applications of uracil-based polycondensed heterocycles.