Rhodium-Catalyzed Anti-Markovnikov Intermolecular Hydroalkoxylation of Terminal Acetylenes

Abstract

We report here the first transition-metal-catalyzed anti-Markovnikov intermolecular hydroalkoxylation of terminal acetylenes to give enol ethers in high yields without using bases. Arylacetylenes as well as alkenyl- and alkylacetylenes were coupled with aliphatic alcohols, and the products were obtained with high Z selectivity in most cases. Effective catalysts were 8-quinolinolato rhodium complexes, which are structurally simple but have been relatively unexplored as catalysts.

A Triflamide‐Tethered N‐Heterocyclic Carbene–Rhodium(I) Catalyst for Hydroalkoxylation Reactions: Ligand‐Promoted Nucleophilic Activation of Alcohols

“…The endo/exo-dig cyclic products are accessed throughi ntramolecular heteroannulations (Scheme 1). [10] In most cases, the products were obtained with high Z selectivity. [3] Enol ethers are important functionalities in organic synthesis and are used widely in cross-coupling,r ing-closing metathesis, and cycloaddition reactions and for the synthesis of pharmaceuticals.…”

“…[1] Significant advancements have been made toward selective formation of the Markovnikov/anti-Markovnikov products for the direct intermolecular addition of amines,a cids, thiols, and various other nucleophilic substrates to alkynes. [10] In most cases, the products were obtained with high Z selectivity. [2] However,addition reactions of weak nucleophiles such as water and alcohol remain achallenging task.…”

“…[7] Kirchner reported the addition of allylic alcohols to phenylacetylene by using the [RuCl{tris(pyrazolyl)borate}(pyridine) 2 ]c atalyst. [10] In most cases, the products were obtained with high Z selectivity. [9] Kakiuchif irst reported the intermolecular anti-Markovnikov hydroalkoxylation of terminal acetylenes by using an 8-quinolinolato-ligated rhodium(I) dicarbonyl complex.…”

“…However, the use of the amide-baseds olvents dimethylformamide and N,N-dimethylacetamide (DMAc) led to ac onsiderable increase in product formation. [10] The prerequisite of pacidic carbonyl ligands for catalyst activity could be rationalized owing to their ability to favor metal-vinylidene formation and to increaset he electrophilicity of the vinylidenec arbon atom. The CÀOb ond formation took place regioselectively at the terminal carbon atom of the phenylacetylene, and the E isomer was the major product.…”

Rhodium-Catalyzed Dimerization of Arylacetylenes and Addition of Malonates­ to 1,3-Enynes

“…Our group has recently reported anti-Markovnikov addition of alcohols, 11 secondary amines 12 as well as the [2+2] cycloaddition of electron-deficient alkenes 13 to terminal alkynes catalyzed by 8-quinolinolato rhodium complex systems. During the course of these studies, the formation of alkyne oligomers as by-products was observed.…”