Construction Of Enantioenriched 2,3-dihydrofuran And Thiochromane-fused Isotetronic Acid Via Michael-addition-initiated Cascade Reaction

Firstly,we have established a highly stereoselective annulation protocol to construct 2,3-dihydrofurans.In the presence of a bifunctional squaramide,the Michael additionalkylation process occurred smoothly to generate the desired 2,3-dihydrofurans in moderate to good isolated yields(33-92%)as trans-diastereomers.It clearly suggested that nitro group could be well used as a leaving group in the enantioselective cascade process.Notably,it is the first example based on replacement of nitro group in the asymmetric process.This catalytic protocol was compatible with a range of structurally distinct gem-benzoyl-nitrostyrenes and 1,3-dicarbonyl compounds.Moreover,further synthetic manipulation of the products were demonstrated as well.Meanwhile,a new type of doubly annulative strategy has been successfully established to construct thiochromane-fused isotetronic acid in a highly enantioenriched fashion mediated by a bifunctional squaramide.The sulfa Michaelaldol-lactonization cascade reaction occurred properly to afford the expected cyclization product in moderate to good isolated yields(52-99%)as a single diastereomer.It clearly indicated that three reactive site of β,γ-unsaturated α-ketoester could be simultaneously utilized in one-pot operation,thereby providing an appealing opportunity to straightforward create polycyclic compounds.The resulting products readily underwent further modification to construct diverse functionalized compounds.