Oxygenated five-membered rings are common and recurring motifs in biologically active compounds. Therefore, the development of routes to synthesize these ring systems is of great interest. Recently, Chang et al. Developed a one-pot (3+2) annualization method to synthesize 3-sulfonyl dihydrofurans (Equation 1).1 This method uses readily available and relatively inexpensive CuI and DMSO to give excellent yields of functionalized dihydrofurans.
Equation 1: CuI/DMSO-mediated synthesis of 3-sulfonyl dihydrofurans
This route is for various types of Ar. works well with1 group, i.e., 4-no2 and 4-OCH3 Replaced phenyl rings. The reaction moved the electron-withdrawing and electron-donating groups to the R position, that is, 4-MeOC. but also tolerated6h4 and 4-FC6h4, Ar. for2, both a phenyl group and a 4-trifluorophenyl group gave similar yields. However, it was found that an aromatic system was necessary in Arro.2 No dihydrofuran as the condition was created when Ar2 was replaced by a hydrogen atom.
These researchers tried several solvents and found that DMSO gave better yields for this reaction. They concluded that DMSO provided better solubility for CuI than the other solvents investigated. Based on previous reports of direct alkylation of activated methylene with the aid of metal addition, the authors proposed the following mechanism (Scheme 1).
In this system, Cu2+ It is believed to help in the oxidation of iodide to iodine. Iodine then assists in the formation of carbocation species. a, Copper is also thought to coordinate to enhance enolate formation. enolate b then reacts with a to make compound C, The iodine then interacts with the alkene bond C produce D which loses a proton and is cycled to form the product I,
Scheme 1: Proposed mechanism for the formation of dihydrofuran.
In conclusion, Chang’s group has achieved excellent yields for this (3+2) annealing to form interesting sulfonyl dihydrofurans. The reaction requires only readily available CuI and DMSO and can be run under air.
Debra D. Dolliver, Ph.D.
- Hsuh N.-C., Hsiao Y.-T., Chang, M.-Y. tetrahedral 2017; 73:4398-4406.