Remarkable facilitation of hetero-cycloisomerizations with water and other polar protic solvents: metal-free synthesis of indolizines.

Hetero-cycloisomerization reactions of propargylic alcohol derivatives leading to indolizines have been demonstrated to proceed in the presence of water alone. This stands as a significant advance over the previous methods using Pt, Cu or Ag salts paired with ligands in organic solvents such as benzene, acetonitrile or methylene chloride.