Asymmetric Catalytic [2,3] Stevens and Sommelet–Hauser Rearrangements of α‐Diazo Pyrazoleamides with Sulfides

Stereoselective Synthesis of Polysubstituted Conjugated Dienes Enabled by Photo-Driven Sequential Sigmatropic Rearrangement

We here reported a highly stereoselective method for the synthesis of polysubstituted conjugated dienes from α-aryl α-diazo alkynyl ketones and pyrazole-substituted unsymmetric aminals under mild conditions, which was promoted by photo-irridation and involved with 1,6-dipolar intermediate and quadruple sigmatropic rearrangements, was successfully developed. In this transformation, the cleavage of four bonds and the recombination of five bonds were implemented in one operational step. This protocol provided a modular tool for constructing dienes from amines, pyrazoles and α-alkynyl-α-diazoketones in one-pot manner. The results of mechanistic investigation indicated that the plausible reaction path underwent the 1,6-sigmatropic rearrangement instead of the 1,5-sigmatropic rearrangement.

Copper-Catalyzed Enantioselective Doyle-Kirmse Reaction of Azide-Ynamides via α-Imino Copper Carbenes

[2,3]-Sigmatropic rearrangement reaction involving sulfonium ylide (Doyle-Kirmse reaction) generated from metal carbenes represents one of the powerful methods for the construction of C(sp³ )-S and C-C bonds. Although significant advances have been achieved, the asymmetric versions via the generation of sulfonium ylides from metal carbenes have been rarely reported to date, and they have so far been limited to diazo compounds as metal carbene precursors. Here, we describe a copper-catalyzed enantioselective Doyle-Kirmse reaction via azide-ynamide cyclization, leading to the practical and divergent assembly of an array of chiral [1,4]thiazino[3,2-b]indoles bearing a quaternary carbon stereocenter in generally moderate to excellent yields and excellent enantioselectivities. Importantly, this protocol represents a unique catalytic asymmetric Doyle-Kirmse reaction via a non-diazo approach and an unprecedented asymmetric [2,3]-sigmatropic rearrangement via α-imino metal carbenes.

Asymmetric Catalytic (2+1) Cycloaddition of Thioketones to Synthesize Tetrasubstituted Thiiranes

Herein, we report the first example of enantioselective (2+1) cycloaddition of thioketones with α-diazo pyrazoleamides for the direct synthesis of tetrasubstituted thiiranes. In the presence of chiral N,N'-dioxide/cobalt(ΙΙ) complexes (2-5 mol%), excellent efficiency (up to 99 % yield within 15 mins) and high stereoselectivity (up to >19 : 1 dr and 97 % ee) are available. Elaborations of thiiranes via desulfuration have also been conducted to deliver tetrasubstituted olefins. Density functional theory calculations reveal that the reaction initiates from a doublet state cobalt(ΙΙ) carbenoid, which is followed by a quartet cobalt(ΙΙ)-bound thiocarbonyl ylide pathway. This work provides a route for the selective construction of tetrasubstituted thiiranes and olefins that are otherwise difficult to access.

Copper-Catalyzed Asymmetric Diyne Cyclization via [1,2]-Stevens-Type Rearrangement for the Synthesis of Chiral Chromeno[3,4-c]pyrroles

Here, we report a copper-catalyzed asymmetric cascade cyclization/[1,2]-Stevens-type rearrangement via a non-diazo approach, leading to the practical and atom-economic assembly of various valuable chiral chromeno[3,4-c]pyrroles bearing a quaternary carbon stereocenter in generally moderate to good yields with wide substrate scope and excellent enantioselectivities (up to 99 % ee). Importantly, this protocol not only represents the first example of catalytic asymmetric [1,2]-Stevens-type rearrangement based on alkynes but also constitutes the first asymmetric formal carbene insertion into the Si-O bond.

Allylsilane Reagent-Controlled Divergent Asymmetric Catalytic Reactions of 2-Naphthoquinone-1-methide

Herein, the first allylsilane reagent-controlled divergent asymmetric Hosomi-Sakurai conjugate allylation and hetero-Diels-Alder (HDA) with 2-naphthoquinone-1-methide (2-Nap-Q-1-M) under the catalysis of Sc^III /Feng ligand complex is reported. With these methods, a variety of uniquely substituted chiral allyl-functionalized diaryl compounds and naphthopyran products were obtained in a straightforward and highly stereoselective (up to 96.5:3.5 e.r.) manner under mild conditions. Moreover, it is demonstrated that 2-Nap-Q-1-M can serve as an efficient diene for a side asymmetric Diels-Alder (D-A) reaction. This principle can provide a straightforward access to hydrophenalene in an optically active form, which represents a structural core of various natural products and bioactive molecules.