Several chiral BINOL-derived bisoxazoline (BOX)/copper(II) complexes were synthesizeda nd evaluated as catalysts for the Friedel-Crafts reaction of indoles with isatin-derived b,g-unsaturated a-keto esters. Ther esulting bis-indole productsb earing aq uaternary stereocenter were obtained in excellent yields and enantioselectivities.A dditionally,t he desired productsw erep ractically transformed to aamino esters, a-hydroxye sters and a-keto amides.I t is noteworthy that this catalytic procedure was conducted with ac atalyst loadingo f0 .5 mol% without any discernible decrease in the reactivity or enantioselectivity.
A cascade asymmetric Michael–intramolecular aldol‐lactonization of enals with oxindolyl β,γ‐unsaturated α‐keto esters was developed. An optically pure aminoindanol‐derived triazolium‐based N‐heterocyclic carbene was used as the catalyst. The corresponding desired β‐propiolactone‐fused spiro[cyclopentane‐oxindoles] were obtained in moderate yields with excellent diastereoselectivities and enantioselectivities. Notably, the obtained enantio‐enriched highly functionalized complex molecules contain four contiguous stereocenters, including a spiro all‐carbon center and a quaternary carbon center.magnified image
An enantioselective formal thio[3 + 3] spiroannulation reaction of indoline-2-thiones to 1-azadienes has been developed by the use of a quinine-derived bifunctional tertiary amine-thiourea catalyst, which furnished a series of optically active spiro[thiopyranoindole-benzoisothiazole] heterocycles with a spiro quaternary C-N/C-S stereogenic centers in high yields with good to excellent diastereo- and enantioselectivities.
A bis-ProPhenol zinc complex-catalyzed asymmetric desymmetrizing intramolecular aldol or aldol condensation reaction is reported, which furnishes spiro[cyclohexanone-oxindole] derivatives in good yields with moderate to high enantioselectivities.
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