FeCl₃/ZnI₂-Catalyzed regioselective synthesis of angularly fused furans

Abstract

The FeCl/ZnI-catalyzed synthesis of angularly fused furans by intermolecular coupling between enols and alkynes has been developed in ambient air. The methodology is successfully applicable to 4-hydroxycoumarin, 4-hydroxyquinolinone and α-tetralone affording regioselective 2-aryl furans in good yields. The control experiments suggest the possibility of a radical reaction mechanism.

Furo[3,2-c]coumarins carrying carbon substituents at C-2 and/or C-3. Isolation, biological activity, synthesis and reaction mechanisms

“…Intermolecular processes. The group of Zha recently described a regioselective oxidative cyclization of 4hydroxycoumarin-derived hypervalent iodine reagents (63) 50 with propiolic acids (64) in the presence of silver I oxide and a rhodium catalyst (Scheme 6) as a valid strategy for accessing the furo[3,2-c]coumarin derivatives (65).…”

“…Dey and Hajra developed an aerobic synthesis of angularly fused furans catalyzed by FeCl 3 /ZnI 2 (Scheme 10), by intermolecular coupling between enols and alkynes as 69. 65 This methodology was applied to 4-hydroxycoumarin (59) providing regioselectively good to very good yields of the furan derivatives 70. Other active methylene compounds were also successfully tested.…”

Recent Advances on Sustainable Synthesis of Furocoumarins

“…During the mechanistic investigation, it was noticed that when the C-3 alkylated product was heated with toluene at 110°C in the presence of catalytic PPh 3 (20 mol%) no desired product formation was achieved but when a mixture of C-3 alkylated product, allenoates and 20 mol% PPh In the year 2017, Alaknanda Hajra et al reported the regioselective synthesis of angularly fused furans by performing a coupling reaction between arylacetylene and 4-hydroxycoumarin in DMSO at 130°C in the presence of FeCl 3 as catalyst and ZnI 2 as an additive under ambient air [Scheme 32]. [75] When the reaction was carried out using the same optimized conditions in the presence of radical initiators such as DDT, BHC, and TEMPO no desired product was obtained which reflects the possibility of involvement of the radical pathway. The plausible mechanism is outlined in Scheme 33.…”

“…In the year 2017, Alaknanda Hajra et al . reported the regioselective synthesis of angularly fused furans by performing a coupling reaction between arylacetylene and 4‐hydroxycoumarin in DMSO at 130°C in the presence of FeCl 3 as catalyst and ZnI 2 as an additive under ambient air [ Scheme 32 ] [75] . When the reaction was carried out using the same optimized conditions in the presence of radical initiators such as DDT, BHC, and TEMPO no desired product was obtained which reflects the possibility of involvement of the radical pathway.…”