Copper(II) Triflate‐Catalyzed Nucleophilic Substitution of Propargylic Acetates with Enoxysilanes. A Straightforward Synthetic Route to Polysubstituted Furans

Abstract

A novel and efficient procedure for the synthesis of g-alkynyl ketones by the nucleophilic substitution of propargylic acetates with enoxysilanes in the presence of a catalytic amount of Copper(II) triflate, has been developed. The substitution reaction can be followed by a 4-toluenesulfonic acid-catalyzed cyclization without purification of the g-alkynyl ketone intermediates, offering a straightforward synthetic route to polysubstituted furans.

Transition Metal-Mediated Synthesis of Monocyclic Aromatic Heterocycles

“…253 The use of a one-pot sequential Cu(II)-catalyzed nucleophilic substitution of propargylic acetates 2-515 with silyl enol ethers 2-516 to give the γ-alkynyl ketones allowed for a subsequent Cu(II)-catalyzed cycloisomerization of the latter upon addition of the p -toluenesulfonic acid co-promoter. It was shown that tri-, tetrasubstituted, as well as fused alkyl- or arylfurans 2-517 bearing various functionalities could be synthesized in high yields.…”

CC Bond Formation with Carbon Dioxide Promoted by a Silver Catalyst

“…However, the b-ketocarboxylic acid products are thermodynamically unstable, therefore only limited types of substrates could be used, as otherwise the product readily converts back into the starting substrate by decarboxylation. Palladium, copper, and gold(I) salts, which were expected to activate the CÀC triple bond, hardly worked for this reaction ( derivative 3 a, [12] which would be formed by the direct intramolecular cyclization of the enol derived from ketone 1 a, was obtained in 13 % yield although the desired product was not obtained at all (Table 1, entry 6). [9] Based on X-ray analysis and NOE experiments, it was suggested that all cyclic carbonates possessed a Z olefin.…”

“…When the catalyst loading was decreased to from 20 mol % to 10 mol %, the reaction of ketone 1 a with carbon dioxide gave the lactone 2 a in good yield (Table 3, entry 2), although a longer reaction time was needed for the reaction to go to completion. Substrates derived from aromatic ketones were subjected to this catalytic system under the optimized reaction conditions ( Table 3, entries [9][10][11][12][13][14]. Substrates derived from aromatic ketones were subjected to this catalytic system under the optimized reaction conditions ( Table 3, entries [9][10][11][12][13][14].…”

“…The postulated reaction with carbon dioxide through CÀC bond formation. The reactions of other methoxyacetophenone derivatives 1 k and 1 l proceeded in the presence of AgOBz (40 mol %) at 10 8C under 2.0 MPa CO 2 pressure and the corresponding products (2 k and 2 l) were obtained in good yields (Table 3, entries [12][13]. The substrate bearing a p-trifluoromethylbenzoyl group 1 i was also a good substrate, producing the corresponding product 2 i in good yield, although a longer reaction time and low reaction temperature were required (Table 3, entry 10).…”

Transition Metal‐Catalyzed Synthesis of Monocyclic Five‐Membered Aromatic Heterocycles

“…Zhan also utilized a similar approach for the 3 þ 2 synthesis of furan compounds from propargylic esters and carbon-centered nucleophiles, overcoming the limitation of Hidai and Uemuras protocol for terminal alkynes (Scheme 8.74) [226]. Employment of a one-pot sequential Cu(II)-catalyzed nucleophilic substitution of propargylic acetates 201 with silyl enol ethers 202 to give the c-alkynyl ketones allowed subsequent Cu(II)-catalyzed cycloisomerization of the latter upon addition of the p-toluenesulfonic acid co-promoter.…”