Base‐ and Copper‐Catalyzed Intramolecular Cyclization for the Direct Synthesis of Dihydrofurans

Abstract

A simple and convenient synthetic approach to dihydrofurans has been developed from the cyclization of 2-propynyl-1,3-dicarbonyl compounds catalyzed by potassium tert-butoxide, copper(II) trifluoromethanesulfonate and triphenylphosphine using methanol/dichloromethane as the solvent under very mild conditions. Moreover, dihydrofurans could be easily transformed into the corresponding furans in the presence of trifluoroacetic acid.

Bi(OTf)3-Mediated Cycloisomerization of γ-Alkynyl Arylketones: Application to the Synthesis of Substituted Furans

“…Furthermore, α-alkylation of 9a – b provided 10a – c in good yields (88%–92%) for generating the skeleton of 2-arylfuran with a 3-electronwithdrawing group (see eq 2, Scheme ). With 10a – c in hand, Bi­(OTf) 3 -mediated cycloisomerization of γ-alkynones 10a – c with the α-ester and benzoyl groups in the presence of molecular sieve in MeNO 2 at rt for 3 h afforded furans 11a – c in 60–81% . In particular, 12 was isolated in a 25% yield via an intramolecular aldolization of the resulting benzoyl δ-diketone of 10c .…”

Progress in Cyclizations of 4‐Acetylenic Ketones: Synthesis of Furans and Pyrroles

“…They proposed the mechanism for this cyclization as shown in Scheme 30. [54] First, enolate 153 was formed from 2-propynyl-1,3-dicartbonyl compounds 151 catalyzed by potassium tert-butoxide. Subsequently, the enolate oxygen anion attacked the carbon-carbon triple bond which was activated by [Cu] 2 + to generate a vinyl-copper adduct 155.…”

La(OTf)3 catalyzed synthesis of α-aryl tetrasubstituted pyrroles through [4+1] annulation under microwave irradiation

“…We chose propargylated β-ketoester 1a and amine 1b as model substrates. In order to avoid the competitive reaction of oxacyclization 11 , excess amount of amine was used at first. As shown in Table 1, screen of Lewis acid and solvents demonstrated that La(OTf) 3 and PhCF 3 are most effective as catalyst and solvent respectively (entries 1-9).…”