19983-83-6Relevant articles and documents
Acetylenes as Potential Antarafacial Components in Concerted Reactions. Formation of Pyrroles from Thermolyses of Propargylamines, of a Dihydrofuran from a Propargylic Ether, and of an Ethylidenepyrrolidine from a β-Amino Acetylene
Viola, Alfred,Collins, John J.,Filipp, Nicholas,Locke, John S.
, p. 5067 - 5075 (2007/10/02)
A thermal cyclization of acetylenic compounds provides evidence for the ability of acetylenic links to act as antarafacial components in processes.The cyclization competes with the normally favored acetylenic retro-ene reaction.Propargylic amines, without substituents whose presence would hinder a tight cyclic transition state, yield intermediate pyrrolines whose subsequent hydrogen elimination affords pyrroles in small amounts.The same process in 2-ethynyltetrahydropyran affords 8-oxabicyclooctane in 35percent yield.A related thermal reaction of N-methyl-3-hexyn-1-amine provides a quantitative transformation to N-methyl-2-ethylidenepyrrolidine in a nominal s + 2a + 2s + 2s> Moebius process, wherein the acetylenic unit is the antarafacial component.Evidence for concertedness in these reactions is discussed.
Thermolysis of Polyazapentadienes. Part 8. The formation of Pyrroles from 1,1-Dialkyl-5-aryl-1,5-diazapentadienes
McNab, Hamish,Murray, M. Elizabeth-Ann
, p. 333 - 338 (2007/10/02)
Flash vacuum pyrolysis of the 1,5-diazapentadienes (4)-(10) gave moderate yields of pyrroles together with quinolines, formed by electrocyclic ring closure with elimination.The pyrroles were formed by hydrogen transfer from an N-alkyl group, followed by cyclisation and final aromatisation of the resulting dihydropyrrole intermediate by free-radical cleavage.The mechanism of the hydrogen transfer and cyclisation is not known with certainty, but may involve diradicals or 1,5-dipolar intermediates.
