1,3‐Dipolar Cycloreversions

Abstract

The 1,3-dipolar cycloreversion reaction represents a general scheme of fragmentation of pentaatomic heterocycles to produce 1,3-dipolar systems and dipolarophiles. This review summarizes cycloreversions which give rise to octet-stabilized 1,3-dipoles. The reaction can be either thermal or photochemical or electron impact induced. The aim of the article is to survey the published results, to emphasize the synthetic potential of this reaction, and to stimulate the study of its several not yet unambiguously defined mechanistic aspects. Scheme 1. 1.3-Dipolar cycloadditions and cycloreversions. Above: reactions with 1,3-dipoles of ally1 type. Below: Reactions with 1,3-dipoles of propargyl-allenyl type. In the reactant shown at top left of scheme, all [5-.3+2]-fragmentations are apriori possible. (a)-(e), see text.

Development of a Hydrazine-Catalyzed Carbonyl-Olefin Metathesis Reaction

“…Crucially, though few in number, examples also exist of the retrocycloaddition of pyrazolidines. [45][46][47] For example, it was shown that cycloreversion of the ketone 137 could be accomplished by heating in xylenes over extended periods of time (Scheme 29a). 46b The resulting azomethine imine 138 was trapped by cycloaddition with norbornene (48) to furnish adduct 140 in 52% yield.…”

Ruthenium and Iron‐Catalysed Decarboxylative N‐alkylation of Cyclic α‐Amino Acids with Alcohols: Sustainable Routes to Pyrrolidine and Piperidine Derivatives

“…whereas oxazolidone/iminium equilibria were proposed during mechanistic studies of proline‐mediated aldol condensation reactions . Decarboxylation of thermally labile oxazolidin‐5‐one derivative ( IV′a ) furnishes azomethine ylides ( Va and Vb ) in a dipolar [3+2] cycloreversion step, as also discussed in literature for various oxazolidinone derivatives . As a final step, the azomethine ylides would undergo protonation and subsequent reduction by means of the metal hydride generated during the first dehydrogenation step, leading to the formation of the N ‐alkylated cyclic amine product ( VI ).…”

Ring-opening carbonyl–olefin metathesis of norbornenes

“…1d). On the other hand, relatively little work has been done regarding [3 + 2]cycloreversions generally, 32 or azomethine imine cycloreversions specically, 33,34 and so it was not clear to what extent such an undertaking would be successful. Nevertheless, we felt that gaining a deeper understanding of the catalyst and condition parameters that control the efficiency of hydrazine-catalyzed COM held great promise to make advancements in this area.…”