Asymmetric synthesis of bicyclic dihydropyrans via organocatalytic inverse-electron-demand oxo-Diels–Alder reactions of enolizable aliphatic aldehydes

An unprecedented highly enantioselective amine catalyzed oxo-IEDDA reaction of cyclic enones with enolizable aldehydes including aqueous acetaldehyde has been developed.

Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate

Stable carbocations such as tritylium ions have been widely explored as organic Lewis acid catalysts and reagents in organic synthesis. However, achieving asymmetric carbocation catalysis remains elusive ever since they were first identified over one century ago. The challenges mainly come from their limited compatibility, scarcity of chiral carbocations, as well as the extremely low barrier to racemization of chiral carbenium ions. We reported here a latent concept for asymmetric carbocation catalysis. In this strategy, chiral trityl phosphate is employed as the carbocation precursor, which undergoes facile ionic dissociation upon mild external stimulation (e.g., acid, H-bonding, polar substrates) to form a catalytically active chiral ion pair for substrate activation and chiral induction. The latent strategy provides a solution for the long sought-after asymmetric carbocation catalysis as illustrated in three different enantioselective transformations.

A Highly Efficient Chirality Switchable Synthesis of Dihydropyran-Fused Benzofurans by Fine-Tuning the Phenolic Proton of β-Isocupreidine (β-ICD) Catalyst with Methyl

A highly enantioselective β-isocupreidine (β-ICD) catalyzed synthesis of dihydropyran-fused benzofurans through [4+2] cycloaddition of allenoates and benzofuranone alkenes was developed. Switchable chirality inversion of cycloaddition products was achieved by replacing the phenolic proton of the catalyst with a methyl, demonstrating an amazing effect of minimal structural variation on inverting enantioselectivity. DFT calculations were utilized to elucidate the origin of the observed phenomena. Computation also provided a clue for a rational design in which the multi-hydrogen bond with the alcohol additive was found to improve the enantioselectivity of the cycloaddition. Finally, the substrate scope was examined, in which a number of functionalized dihydropyran-fused benzofurans could be obtained in high yields (up to 97 %) with very good regio- (>20:1) and enantioselectivities (up to 98:2 e.r.).

[4 + 2] cycloaddition of in situ generated 1,2-diaza-1,3-dienes with simple olefins: facile approaches to tetrahydropyridazines

A catalyst-free [4 + 2] annulation process between in situ generated 1,2-diaza-1,3-butadienes and simple olefins has been developed. Under mild conditions, the reactions afforded 1,4,5,6-tetrahydropyridazines, which feature a wide range of bioactive compounds, with high yields (up to 99% yield).

The N,N′-dioxide/Ni(ii)-catalyzed asymmetric inverse-electron-demand hetero-Diels–Alder reaction of methyleneindolinones with hetero-substituted alkenes

The asymmetric inverse-electron-demand hetero-Diels–Alder reaction of methyleneindolinones with hetero-substituted alkenes catalyzed by chiral N,N′-dioxide/Ni(ii) complexes has been accomplished, affording dihydropyran-fused indoles in up to 99% yield, >95 : 5 dr and 99% ee.

Reversal of enantioselective Friedel–Crafts C3-alkylation of pyrrole by slightly tuning the amide units of N,N′-dioxide ligands

Reversal enantioselective Friedel-Crafts alkylation of pyrrole with ligands derived from the same type of chiral source of L-ramipril, by slightly tuning the amide units has been realized.

A catalytic asymmetric carbonyl–ene reaction of β,γ-unsaturated α-ketoesters with 5-methyleneoxazolines

A catalytic asymmetric carbonyl–ene reaction of β,γ-unsaturated α-ketoesters with 5-methyleneoxazolines was accomplished. The process was based on the utilization of a chiral N,N′-dioxide/Mg^II catalyst, providing the desired products with excellent outcomes.

Stereo-controlled synthesis of polyheterocycles via the diene-transmissive hetero-Diels–Alder reaction of β,γ-unsaturated α-keto esters

Stereocontrolled synthesis of polyheterocycles via the diene-transmissive hetero Diels–Alder reaction of β,χ-unsaturated α-keto esters is described.

N,N'-dioxide/nickel(II)-catalyzed asymmetric inverse-electron-demand hetero-diels-alder reaction of β,γ-unsaturated α-ketoesters with enecarbamates

N,N'-Dioxide/nickel(II) complexes have been developed to catalyze the inverse-electron-demand hetero-Diels-Alder reaction of β,γ-unsaturated α-ketoesters with acyclic enecarbamates. After detailed screening of the reaction parameters, mild optimized reaction conditions were established, affording 3,4-dihydro-2H-pyranamines in up to 99 % yield, 99 % ee and more than 95:5 d.r. The catalytic system was also efficient for β-substituted acyclic enecarbamates, affording more challenging 2,3,4-trisubstituted 3,4-dihydro-2H-pyranamine with three contiguous stereogenic centers in excellent yields, diastereoselectivities, and enantioselectivities. The reaction could be scaled up to a gram scale with no deterioration of either enantioselectivity or yield. Based on these experiments and on previous reports, a possible transition state was proposed.

Synthesis of spiroaminals by bimetallic Au/Sc relay catalysis: TMS as a traceless controlling group

An efficient synthesis of spiroaminals over fused aminals has been successfully developed by bimetallic Au/Sc catalysis by using TMS as a traceless controlling group.