An Improved Synthesis of 2-Nitrobenzo[<i>b</i>]furans
作者:Anne Tromelin、Pierre Demerseman、René Royer
DOI:10.1055/s-1985-31435
日期:——
2-Nitrobenzo[b]furans 4 are prepared in improved yields by reacting o-hydroxybenzaldehydes 1 and bromonitromethane (2) at low temperature in order to avoid the dehydration of the aldol intermediate 3 in the alkaline condensation medium. This aldol 3 is then quantitatively dehydrated by heating in acetic anhydride.
phosphine-catalyzed asymmetric dearomative [3+2] cycloaddition of 2-nitrobenzofurans with aldehyde-derived Morita–Baylis–Hillman (MBH) carbonates or allenoate was developed. The reaction with MBH carbonates resulted in a series of cyclopentabenzofurans containing three contiguous stereocenters with good to high yields, diastereoselectivities and enantioselectivities. The use of allenoate also gave the target product
Regio‐ and Stereoselective Cascade of β,γ‐Unsaturated Ketones by Dipeptided Phosphonium Salt Catalysis: Stereospecific Construction of Dihydrofuro‐Fused [2,3‐b] Skeletons
作者:Hongkui Zhang、Jiajia He、Yayun Chen、Cheng Zhuang、Chunhui Jiang、Kai Xiao、Zhishan Su、Xiaoyu Ren、Tianli Wang
DOI:10.1002/anie.202106046
日期:2021.9
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 Brønstedacid moieties
A straight synthetic approach to fused polycyclic tropane scaffold formation through an asymmetric dearomatization cycloaddition process of 2-nitrobenzofurans with cyclic azomethineylides was successfully developed. In the presence of a chiral copper complex, derived from Cu(OAc)2 and a diphosphine ligand, a series of fused polycyclic tropane derivatives were obtained in high yields (75-91%) with
dearomative cycloaddition of 3‐nitroindoles and 2‐nitrobenzofurans have emerged as a powerful protocol to construct chiral fused heterocyclic rings. However, organocatalytic dearomative reaction of these two classes of heteroarenes has become a long‐standing challenging task. Herein, we report the first example of phosphine‐catalyzed asymmetric dearomative [3+2]‐cycloadditio of 3‐nitroindoles and 2‐nitrobenzofurans