Fast and Efficient Synthesis of Z‐Enol‐γ‐Lactones through a Cycloisomerization Reaction of β‐Hydroxy‐γ‐Alkynoic Acids Catalyzed by Copper(I) under Microwave Heating in Water

Abstract

Ad iastereo-and regioselective methodf or accessing av ariety of highly functionalized Z-enol-g-lactones in good yields through the cycloisomerization of b-hydroxy-galkynoic acids catalyzed by CuBr (5 mol %) in water under microwaveh eating in as hort time is described.

Copper Catalyzed Synthesis of Heterocyclic Molecules via C–N and C–O Bond Formation under Microwaves: A Mini-Review

“…The cycloisomerization of compound 67 catalyzed by CuBr (5 mol %) in water under microwave irradiation at 100 °C for 8 min was presented a diastereo and regioselective approach for gaining access to a wide range of highly functionalized lactones 68 in excellent yields (Scheme ). For a wide range of highly functionalized compound 68 , this approach allows for high yields under moderate reaction conditions …”

Reactions of Bis(trimethylsilyl)ketene Acetals with Several Activated Organic Substrates

“…A diastereo‐ and regioselective method for accessing a variety of highly functionalized ( Z )‐enol‐γ‐lactones 104 (5‐ exo ‐ dig products) in good yields through the cycloisomerization of β‐hydroxy‐γ‐alkynoic acids 100 , catalyzed by CuBr (5 mol‐%) in water under microwave heating conditions, has also been described, Scheme …”

Metal-Catalyzed Intra- and Intermolecular Addition of Carboxylic Acids to Alkynes in Aqueous Media: A Review

“…On the other hand, although the mechanism could not be unambiguously established, it was assumed that the Cu 2+ ion is the one responsible for the activation of the alkyne unit during the final cycloisomerization step, with Fe 3+ probably facilitating the intramolecular nucleophilic addition of the carboxylate on the C≡C bond by coordination to the carbonyl group. More recently, CuBr was also employed to promote the cyclization of a variety of β-hydroxy-γ-alkynoic acids 17 [50]. As shown in Scheme 10, the reactions proceeded cleanly in pure water under microwave (MW) irradiation at 100 • C, leading to the regio-and stereoselective formation of the five membered ring Z-enol-lactones 18 without observing hydrolysis products.…”

“…However, it should be noted that when an alkynoic acid featuring a hydrogen atom and a phenyl group, as the R 3 and R 4 substituents, was employed in this reaction, the spontaneous dehydration of 18 to form a 5-alkylidene-furan-2-one product took place. More recently, CuBr was also employed to promote the cyclization of a variety of β-hydroxy-γ-alkynoic acids 17 [50]. As shown in Scheme 10, the reactions proceeded cleanly in pure water under microwave (MW) irradiation at 100 °C, leading to the regio-and stereoselective formation of the five membered ring Z-enol-lactones 18 without observing hydrolysis products.…”