40024-32-6

Chiral (dihydro)furo-fused heterocycles are significant structural motifs in numerous natural products, functional materials and pharmaceuticals. Therefore, developing efficient methods for preparing compounds with these privileged scaffolds is an important endeavor in synthetic chemistry. Herein, we develop an effective, modular method by a dipeptide-phosphonium salt-catalyzed regio- and stereoselective cascade reaction of readily available linear β,γ-unsaturated ketones with aromatic alkenes, affording a wide variety of structurally fused heterocyclic molecules in high yields with excellent stereoselectivities. Moreover, mechanistic investigations revealed that the bifunctional phosphonium salt controlled the regio- and stereoselectivities of this cascade reaction, particularly proceeding through the initial ketone α-addition followed by O-participated substitution; and the multiple hydrogen-bonding interactions between Br?nsted acid moieties of catalyst and nitro group of aromatic alkene were crucial in asymmetric induction. Given the generality, versatility, and high efficiency of this method, we anticipate that it will have broad synthetic utilities.

Various salicylaldehydes were treated with bromonitromethane in the presence of an inorganic base to give 2-nitrobenzofuran derivatives, and the reaction mechanisms were investigated.The most remarkable feature of the reactions is that 3-hydroxysalicylaldehyde (1k) alone among various hydroxysalicylaldehydes (1b, k, n, r) gave 2-nitro-7-hydroxybenzofuran in good yield.Bromonitromethane reacted with salicylaldehydes at the aldehyde group exclusively to give 1-(2-hydroxyphenyl)-2-bromo-2-nitroethanols (14), followed by cyclization to produce mixtures consisting of cis- and trans-2-nitro-3-hydroxy-2,3-dihydrobenzofurans (8a, b; 9a, b; 10a, b).The stereochemistry of these products is discussed on the basis of the spectral data and chemical reactivities.The intermediates, 2,3-dihydrobenzofurans, underwent dehydration smoothly to give 2-nitrobenzofurans.Keywords - bromonitromethane; salicylaldehyde derivative; ring closure; 2-nitrobenzofuran derivative; cis-2-nitro-3-hydroxy-2,3-dihydrobenzofuran derivative; trans-2-nitro-3-hydroxy-2,3-dihydrobenzofuran derivative; 13C-NMR; stereochemistry; reaction mechanism