Divergent Synthesis of Five-Membered Nitrogen Heterocycles via Cascade Reactions of 4-Arylfuroxans

Abstract

A novel method for the synthesis of a diverse series of functionally substituted five-membered heterocyclic compounds via atom-economic, regio-, and diastereoselective one-pot reaction cascade was developed. This approach involves a ring opening in 4-arylfuroxans to α-oximinoarylacetonitrile oxides followed by [3+2] cycloaddition to various dipolarophiles to afford multisubstituted isoxazoles and isoxazolines. Subsequent azole–azole rearrangement of (oximino)isoxazolines/-isoxazoles, which can be conducted in a one-pot manner, results into functionally substituted furazans formation. The developed protocol is operationally simple, proceeds in mild conditions and with high yields of target heterocyclic systems. Overall, this study represents a new mode of isoxazole and 1,2,5-oxadiazole functionalization strategy, which is useful in medicinal and materials chemistry.

Electrochemical Activation of Nitromethane to Construct Isoxazoline Aldoximes

“…Styrene and product 2 a are hard to be oxidized, displaying high oxidation potentials at 2.53 V and 2.60 V vs Ag/AgCl, respectively, which are similar to the oxidative potential of 1,4-dioxane (E p ox = 2.50 V vs Ag/AgCl). Based on the mechanistic studies and previous reports, [10,22] we proposed the mechanism in Figure 4 using styrene 1 a as a model substrate. The anodic oxidation of I À in n-Bu 4 NI (E p ox = 0.85 V vs Ag/AgCl) produces the iodine radical and I 2 .…”

“…Based on the mechanistic studies and previous reports, [10,22] we proposed the mechanism in Figure 4 using styrene 1 a as a model substrate. The anodic oxidation of I − in n ‐Bu 4 NI ( E p ox =0.85 V vs Ag/AgCl) produces the iodine radical and I 2 [23,24] .…”

Biocatalytic stereoselective synthesis of pyrrolidine-2,3-diones containing all-carbon quaternary stereocenters

“…[1][2][3][4][5][6][7][8][9] Likewise, five-membered nitrogen heterocycles are important due to their numerous biological and pharmacological properties. [10][11][12][13] The combination of these heterocycles with quaternary stereocenters is particularly highly regarded due to their presence in many alkaloids. [14][15][16][17][18][19] The crinane alkaloid family, which belongs to the Amaryllidaceae alkaloids, represents such scaffolds that contain catechol-based substituted five-membered nitrogen heterocycles with all-carbon quaternary stereocenters.…”