Ru-Catalyzed Cyclization of Terminal Alkynals to Cycloalkenes

Abstract

Cycloalkenes can be efficiently prepared by a new Ru-catalyzed cyclization of terminal alkynals. Under appropriate conditions, cycloisomerizations to conjugated aldehydes may be observed. Both processes involve catalytic Ru vinylidenes.

Osmium‐Catalyzed 7‐endo Heterocyclization of Aromatic Alkynols into Benzoxepines

“…[4] More recently, the efficient preparation of indoles by the rhodiumcatalyzed cycloisomerization of 2-(ethynyl)anilines, [5] and the smooth preparation of benzofurans and benzopyrans by the ruthenium-catalyzed 5-endo and 6-endo heterocyclization reactions of substituted (2-ethynyl)phenols and benzylic alcohols, respectively, have been also described. [6,7] On the other hand, the heterocyclization of alkynols into the sevenmembered oxepines, a framework commonly found in complicated polycyclic marine natural products, [8] has only been achieved from specific acetonide-protected alkynol substrates via tungsten-vinylidene complexes. [9] Osmium is more reducing than ruthenium, prefers to be saturated by coordination, and redox isomers with more metal À carbon bonds.…”

Reactions of Aldehydes and Ketones and their Derivatives

“…348 In some cases, cycloisomerization to give conjugated aldehyde occurred. Both processes are believed to involve catalytic ruthenium vinylidenes.…”

Ruthenium-Catalyzed Aldehyde Functionality Reshuffle: Selective Synthesis ofE-2-Arylcinnamaldehydes fromE-β-Bromostyrenes and Aryl Aldehydes

“…Subsequently, nucleophilic addition of water to A generates intermediate B, 11 which undergoes an aldol-type reaction with aldehyde 2 immediately to give intermediate C and regenerate water. 12 Finally, reductive elimination of C gives the final product 3 and regenerates the active ruthenium catalyst. It is also possible that the reductive elimination occurred first or a ruthenium-catalyzed direct conversion of the vinyl halide to generate a phenylacetaldehyde, which undergoes the aldol reaction to give the final product.…”