Stereocontrolled construction of 2-(3-indolyl)chromane scaffolds via organocatalyzed cascade Michael addition-hemiketalization followed by Friedel–Crafts alkylation reaction

The chemistry of 2-hydroxy-β-nitrostyrenes: versatile intermediates in synthetic organic chemistry

“…Although the diastereoselectivity of the reaction is low, excellent diastereoselectivity in products (>20 : 1 dr ratio) can be achieved after purification by recrystallization. 31 In 2019, Deng et al reported a Michael/hemiacetalization cascade reaction of α-ketoesters 44 with 2 in the presence of the Ni(OAc) 2 -Cat-6 complex followed by the acylation reaction with Ac 2 O to afford chiral chromans 46 bearing three continuous stereocenters including one all-substituted carbon stereocenter in good yields (60-89%), up to >20 : 1 diastereoselectivities and high enantioselectivities (92->99% ee) (Scheme 16). 32 Optimized conditions for this reaction include mixing an equivalent of 2 with 1.2 equivalent of 44 in 2-propanol at −20 °C in the presence of 5 mol% of Ni(OAc) 2 -Cat-6 and Et 3 N (10 mol%).…”

“…Although the diastereoselectivity of the reaction is low, excellent diastereoselectivity in products (>20 : 1 dr ratio) can be achieved after purification by recrystallization. 31…”

Kinetic Resolution of Axially Chiral 2‐Nitrovinyl Biaryls Catalyzed by a Bifunctional Thiophosphinamide

“…[9h] Although these strategies have gained substantial progress, the kinetic resolution process is mainly based on the transformation of the phenolic hydroxyl, amino, C=N, vinyl ether and activated halo functionality, and in which no new stereogenic center is generated. Recently, we have proved that primary amine/thiophos-phinamides are efficient catalysts to promote the conjugate addition of acetone to simple [12] and orthohydroxyl [13] or ortho-azido [14] substituted nitroolefins in a highly enantioselective manner. In contrast to the wide application of nitroolefins in asymmetric catalysis, [11] the catalytic kinetic resolution of axially chiral nitroalkenes has surprisingly been unexplored and remains a challenging problem.…”

“…In contrast to the wide application of nitroolefins in asymmetric catalysis, the catalytic kinetic resolution of axially chiral nitroalkenes has surprisingly been unexplored and remains a challenging problem. Recently, we have proved that primary amine/thiophosphinamides are efficient catalysts to promote the conjugate addition of acetone to simple and ortho‐hydroxyl or ortho‐azido substituted nitroolefins in a highly enantioselective manner. We envisioned that this type of catalyst may be able to distinguish the chiral axis of the biaryls to provide high kinetic resolution efficiency.…”

Organocatalytic Enantioselective Friedel–Crafts Aminoalkylation of Indoles in the Carbocyclic Ring

“…Indoles are excellent nucleophiles prone to react by electrophilic aromatic substitution at the C-3 position of the azole ring including enantioselective transformations. Positions C-2 and N-1 can also be functionalized selectively using different strategies …”