Ruthenium-Catalyzed Cyclization of Epoxide with a Tethered Alkyne:  Formation of Ketene Intermediates via Oxygen Transfer from Epoxides to Terminal Alkynes

Abstract

Treatment of (o-ethynyl)phenyl epoxides with TpRuPPh(3)(CH(3)CN)(2)PF(6) (10 mol %) in hot toluene (100 degrees C, 3-6 h) gave 2-naphthols or 1-alkylidene-2-indanones very selectively with isolated yields exceeding 72%, depending on the nature of the epoxide substituents. Surprisingly, the reaction intermediate proved to be a ruthenium-pi-ketene species that can be trapped efficiently by alcohol to give an ester compound. This phenomenon indicates a novel oxygen transfer from epoxide to its terminal alkyne catalyzed by a ruthenium complex. A plausible mechanism is proposed on the basis of reaction products and the deuterium-labeling experiment. The 2-naphthol products are thought to derive from 6-endo-dig cyclization of (o-alkenyl)phenyl ketene intermediates, whereas 1-alkylidene-2-indanones are given from the 5-endo-dig cyclization pathway.

Gold Catalysis: Synthesis of 3‐Acylindenes from 2‐Alkynylaryl Epoxides

“…Furthermore, the fact that internal alkynes react, excludes the participation of vinylidene-metal species as suggested by Liu et al for related reactions of similar substrates with ruthenium catalysts (leading to different products). [9] A mechanistic proposal is shown in Scheme 3. After coordination of the alkyne to the catalyst (17) and electrophilic attack at the oxirane oxygen atom, the benzylic cation 18 could be generated.…”

Metal Vinylidenes as Catalytic Species in Organic Reactions

“…[63] Thus (oethynyl)styrene epoxides such as 134, when treated with catalytic amount of [TpRu(PPh 3 ) (NCCH 3 ) 2 ]PF 6 , lead to 2-naphthol products such as 135 (equation 1, Scheme 42). Higher substituted epoxides (136), however, lead to 1-alkylidene-2-indanones 137 instead (equation 2).…”

Metal Vinylidenes and Allenylidenes in Catalysis: Applications in Anti‐Markovnikov Additions to Terminal Alkynes and Alkene Metathesis

“…[110] In the presence of the same catalyst, 1-iodo-2-naphthol and 2-iodobenzo[d]oxepin can be selectively obtained from iodoalkynes in DMF and benzene, respectively. [111] Tungsten-and chromium-carbonyl complexes activate the terminal triple bond of 1-acyl-2-ethynylcyclopropanes to generate metal vinylidene species, which undergo cyclopropane ring opening and cyclization into a seven-membered oxacycloheptadienylidene by attack of the oxygen atom at the electrophilic vinylidene carbon center.…”