Electrocyclizations of Conjugated Azapolyenes Produced in Reactions of Azaheterocycles with Metal Carbenes

Abstract

Conjugated azapolyenes (azabuta-1,3-dienes, aza-/diaza-/oxaza-/oxadiazahexa-1,3,5-trienes) are highly reactive in electrocyclization reactions, which makes them convenient precursors for the synthesis of a wide range of four-, five-, and six-membered nitrogen heterocycles that are of relevance for medicinal chemistry. Ring opening reactions of 2H-azirines and azoles containing an N–N or N–O bond, initiated by a transition metal carbene, have become increasingly important in recent years, since they easily allow the generation of azapolyenes with different numbers of double bonds and heteroatoms in various positions. This review summarizes the literature, published mainly in the last decade, on the synthetic and mechanistic aspects of electrocyclizations of azapolyenes generated by the carbene method.

One-Pot Synthesis of Multifunctionalized 1-Pyrrolines from 2-Alkyl-2H-azirines and Diazocarbonyl Compounds

“…Given the limitations of existing methods, and as a part of our current interest directed toward the efficient and practical synthesis of nitrogen heterocycles, we aimed in this work at developing a novel synthesis of highly substituted 1-pyrrolines 4 via base-promoted 1,5-cyclization of 4-alkyl-2-azabuta-1,3-dienes 3 (Scheme ), which in turn, could be prepared from 2 H -azirines 1 and diazoesters 2 . Such a strategy to construct 1-pyrrolines is a novel type of [4 + 1] annulations .…”