One-Pot Synthesis of 2-Acetyl-1-pyrroles from -Propargylic β-Enaminones via Intermediacy of 1,4-Oxazepines.

A one-pot two-step protocol for the synthesis of 2-acetyl-1-pyrroles from -propargylic β-enaminones was described. When treated with zinc chloride in refluxing chloroform, -propargylic β-enaminones produced in situ 2-methylene-2,3-dihydro-1,4-oxazepines, which, upon further refluxing in methanol with zinc chloride, afforded 2-acetyl-1-pyrroles. The process was found to be general for a wide variety of -propargylic β-enaminones and yielded a diverse range of 2-acetyl-1-pyrroles in good to high yields with large substrate scope and good functional group tolerance.

A new strategy for the synthesis of pyridines from N-propargylic β-enaminothiones.

A new method for the synthesis of 2,4,5-trisubstituted pyridines from N-propargylic β-enaminothiones is reported. β-Enaminothiones were prepared by thionation of the corresponding β-enaminones with Lawesson's reagent. When treated with diisopropylamine in DMF at room temperature, N-propargylic β-enaminothiones yielded 2,4,5-trisubstituted pyridines in moderate to high yields, along with small amounts of 2-methylene-2,3-dihydro-1,4-thiazepines.

Synthesis of 1,4-Thiazepines.

An efficient, general, and unprecedented methodology for the synthesis of 2-methylene-2,3-dihydro-1,4-thiazepines from N-propargylic β-enaminones is described. Initially, N-propargylic β-enaminones were thionated with Lawesson's reagent in good to high yields, and then the resulting N-propargylic β-enaminothiones were subjected to electrophilic cyclization. When treated with zinc chloride in refluxing chloroform, N-propargylic β-enaminothiones underwent electrophilic cyclization to yield 2-methylene-2,3-dihydro-1,4-thiazepines in good to high yields.