Desymmetrization by Asymmetric Copper-Catalyzed Intramolecular C–H Insertion Reactions of α-Diazo-β-oxosulfones

Organocatalyst-mediated asymmetric one-pot/two domino/three-component coupling reactions for the synthesis of trans-hydrindanes

Highly substituted trans-hydrindanes were synthesized by the three-component coupling reactions of 1,3-diethyl 2-(2-oxopropylidene)propanedioate and two different α,β-unsaturated aldehydes catalyzed by diphenylprolinol silyl ether. The reaction proceeds via two successive independent catalytic domino reactions in a one-pot reaction by a single chiral catalyst. Domino reactions involve Michael/Michael and Michael/aldol reactions to afford trans-hydrindanes with excellent diastereoselectivity and nearly optically pure form.

Catalytic asymmetric C-H insertion reactions of vinyl carbocations

From the preparation of pharmaceuticals to enzymatic construction of natural products, carbocations are central to molecular synthesis. Although these reactive intermediates are engaged in stereoselective processes in nature, exerting enantiocontrol over carbocations with synthetic catalysts remains challenging. Many resonance-stabilized tricoordinated carbocations, such as iminium and oxocarbenium ions, have been applied in catalytic enantioselective reactions. However, their dicoordinated counterparts (aryl and vinyl carbocations) have not, despite their emerging utility in chemical synthesis. We report the discovery of a highly enantioselective vinyl carbocation carbon-hydrogen (C-H) insertion reaction enabled by imidodiphosphorimidate organocatalysts. Active site confinement featured in this catalyst class not only enables effective enantiocontrol but also expands the scope of vinyl cation C-H insertion chemistry, which broadens the utility of this transition metal-free C(sp³)-H functionalization platform.

Dirhodium Carboxylate Catalysts from 2-Fenchyloxy or 2-Menthyloxy Arylacetic Acids: Enantioselective C-H Insertion, Aromatic Addition and Oxonium Ylide Formation/Rearrangement

A new class of dirhodium carboxylate catalysts have been designed and synthesized from 2-fenchyloxy or 2-menthyloxy arylacetic acids which display excellent enantioselectivity across a range of transformations of α-diazocarbonyl compounds. The catalysts were successfully applied to enantioselective C-H insertion reactions of aryldiazoacetates and α-diazo-β-oxosulfones affording the respective products in up to 93 % ee with excellent trans diastereoselectivity in most cases. Furthermore, efficient desymmetrization in an intramolecular C-H insertion was achieved. In addition, these catalysts prove highly enantioselective for intramolecular aromatic addition with up to 88 % ee, and oxonium ylide formation and rearrangement with up to 74 % ee.

Exploiting Continuous Processing for Challenging Diazo Transfer and Telescoped Copper-Catalyzed Asymmetric Transformations

Generation and use of triflyl azide in flow enables efficient synthesis of a range of α-diazocarbonyl compounds, including α-diazoketones, α-diazoamides, and an α-diazosulfonyl ester, via both Regitz-type diazo transfer and deacylative/debenzoylative diazo-transfer processes with excellent yields and offers versatility in the solvent employed, in addition to addressing the hazards associated with handling of this highly reactive sulfonyl azide. Telescoping the generation of triflyl azide and diazo-transfer process with highly enantioselective copper-mediated intramolecular aromatic addition and C–H insertion processes demonstrates that the reaction stream containing the α-diazocarbonyl compound can be obtained in sufficient purity to pass directly over the immobilized copper bis(oxazoline) catalyst without detrimentally impacting the catalyst enantioselectivity.

Domino Synthetic Strategy for Tetrahydrothiopyran Derivatives from Benzaldehydes, 2-Acetylfuran/2-Acetylthiophene, and Sodium Sulfide

A novel domino reaction from benzaldehydes and 2-acetylfuran/2-acetylthiophene with sodium sulfide was developed to synthesize a series of tetrahydrothiopyran (THTP) derivatives. The reaction proceeded well to construct a tetrahydrothiopyran ring and five new bonds in one step. A mechanism is proposed, involving a stepwise Aldol/double Michael addition/Aldol (AMMA) reaction cascade. In this transformation, sodium sulfide acts as a nucleophile and base. This method is characterized by transition-metal-free, commercially available starting materials and mild reaction conditions.

Synthesis and Rhodium(II)-Mediated Cascade Cyclopropanation/Rearrangement/Isomerization of Diazo 2,3,5-Trisubstituted Furans: The Construction of Penta-substituted Aromatic Compounds

Ag(I)-catalyzed synthesis of diazo-trisubstituted furans starting from diazo-cumulated allenyl ketones has been investigated. The Rh₂(OAc)₄-catalyzed reaction of the diazo 2,3,5-trisubstituted furans provided penta-substituted aromatics via cascade intermolecular cyclopropanation/rearrangement/isomerization. The cyclopropanation on the furan ring/rearrangement of cyclopropane moiety has been reported. A reasonable mechanism is proposed.