Catalytic Cycloisomerization-Oxidative Cyclization Reaction Sequence of Enyne Diesters Derived from 2-Propargyloxyarylaldehydes

Enyne diesters derived from 2-propargyloxyarylaldehydes are converted into 2-oxopyranochromenes via In(OTf)3-catalyzed cycloisomerization and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-mediated oxidative cyclization reaction sequence in one pot. The process possesses broad substrate scope and good functional group compatibility and generates various 4-(hetero)aryl-substituted 2-oxopyranochromenes in 32-79% yields (over two steps). 2-Oxopyranochromenes undergo selective decarboxylation under Krapcho conditions. When treated with aliphatic secondary amines in DMF, 2-oxopyranochromenes undergo decarboxylative amination at ambient temperature to generate 2-amino-substituted functionalized chromenes in good yields.

Construction of Diverse Fused Chromene Frameworks via Isocyanide-Based Three-Component Reaction

A convenient synthetic protocol for diverse fused chromenes was successfully developed by a three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and various cyclic 1,3-dipolarophiles containing o-hydroxyphenyl group. In the absence of any catalyst, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and 3-(o-hydroxyarylidene)indolin-2-ones in tetrahydrofuran at 60 °C resulted in unique functionalized spiro[cyclobuta[c]chromene-1,3'-indolines] in good yields and with high diastereoselectivity. However, the similar three-component reaction with 2-(5-halo-2-hydroxyarylidene)indolin-2-ones afforded unexpected chain products in satisfactory yields. In addition, the three-component reaction of alkyl isocyanides, dialkyl but-2-ynedioates, and 2-(o-hydroxyarylidene)-1,3-indanediones in tetrahydrofuran at 60 °C resulted in complex indeno[2',1':5,6]pyrano[3,4-c]chromene derivatives in high yields and with high diastereoselectivity.

Asymmetric Retro-Claisen Reaction Catalyzed by Chiral Aza-Bisoxazoline-Zn(II) Complex: Enantioselective Synthesis of α-Arylated Ketones

An asymmetric retro-Claisen reaction of α-monosubstituted β-diketones and quinones (or quinone imine) has been developed under the catalysis of a chiral aza-bisoxazoline-Zn(II) complex. The reaction proceeds via a sequence of conjugate addition, arylation, hemiketal anion-initiated C-C bond cleavage, and enantioselective protonation of enolate to provide various functionalized α-arylated ketones bearing a tertiary stereogenic center with high enantioselectivities. Notably, biologically important benzofuran and γ-butyrolactone derivatives could be synthesized by application of the developed protocol.

Assembly of fluorinated chromanones via enantioselective tandem reaction

The enantioselective synthesis of fluorinated tricyclic chromanones with multiple vicinal stereogenic centers has been realized for the first time, through the tandem reaction between 2-fluorinated 1-(2-hydroxyaryl)-1,3-diketones and α,β-unsaturated aldehydes. In the presence of chiral amine, the organo-tandem reaction including catalytic Michael addition/cycloketalization/hemiacetalization and acylation sequence provided a wide range of fluorinated tricyclic chromanones with excellent outcomes (>30 examples, up to >99% ee and >19 : 1 d.r.). A plausible catalytic cycle and transition state are also provided for this tandem reaction to rationalize the observed sense of asymmetric induction.

Brønsted acid-catalyzed dynamic kinetic resolution of in situ formed acyclic N,O-hemiaminals: cascade synthesis of chiral cyclic N,O-aminals

A H2O controlled dynamic kinetic resolution was involved in a Brønsted acid-catalyzed acyclic N,O-hemiaminal formation/oxa-Michael reaction cascade, leading to highly enantioenriched cis-2,6-disubstituted tetrahydropyrans bearing an exo amide group.

An asymmetric multicatalytic reaction sequence of 2-hydroxycinnamaldehydes and enolic 1,3-dicarbonyl compounds to construct bridged bicyclic acetals

2-Hydroxycinnamaldehydes and cyclic 1,3-dicarbonyl nucleophiles were used in an asymmetric organocatalyzed reaction sequence to construct bridged bicyclic acetals via a multicatalytic process involving iminium catalysis and anion-binding catalysis.

Application of E1cB Elimination in Asymmetric Organocatalytic Cascade Reactions To Construct Polyheterocyclic Compounds

By introducing a carbon functionality at 2-position of chromane, the formal asymmetric functionalization of the 3-position of 2-substituted chromane has been realized via a highly chemo-, regio-, and stereoselective organocatalytic cascade reaction in a sequential one-pot manner involving an E1cB mechanism governed ring-opening process. Critical to our success was the design of a chiral dipeptide-based bifunctional acid-base organocatalyst, which exhibited high catalytic activity at low catalyst loading (1-0.1 mol %), leading to biologically interesting polyheterocyclic compounds.

The Quinary Catalyst-Substrate Complex Induced Construction of Spiro-Bridged or Cagelike Polyheterocyclic Compounds via a Substrate-Controlled Cascade Process

The asymmetric organocatalytic cascade reaction of cyclic β-oxo aldehydes to 2-hydroxycinnamaldehydes is developed. The bifunctional tertiary amine-thiourea catalyst was used in a rationally designed multiple catalysis where the asymmetric iminium catalysis and thiourea anion-binding catalysis were combined by carboxylate anion as a ternary catalytic system to form a quinary catalyst-substrate complex, providing an efficient protocol for the construction of enantioenriched spiro-bridged or cagelike polyheterocyclic compounds. The reuse of catalysts was also successfully realized.