Rhodium-Catalyzed Enantioselective [4+2] Cycloadditions of Vinylcarbenes with Dienes

HNTf2-Catalyzed Formal [3 + 2] Cycloaddition of Vinyldiazoacetates to Indole-Substituted Diazo Compounds and Their Conversion to Carbazoles

Triflimide catalysis of the [3 + 2]-cycloaddition of 3-indolymethanols with vinyldiazoacetates provides general access to β-tetrahydrocyclopenta[b]indol-substituted α-diazoesters. Initiated by addition of the in situ generated vinylogous iminium electrophile from 3-indolymethanol to the vinylogous position of the vinyldiazo compound and completed by intramolecular cyclization from the vinyldiazonium ion intermediate, this transformation occurs in good yields and excellent diastereoselectivity with a broad substrate scope under mild conditions. The resulting α-diazoesters undergo Rh2(OAc)4-catalyzed substrate-dependent 1,2-migration to form multisubstituted carbazoles in high yields.

Silver-catalyzed pyrazole migration and cycloaddition reaction of diazo pyrazoleamides with ketimines

A novel pyrazole migration and cycloaddition process is well developed via AgOTf-catalyzed annulation reactions of α-diazo pyrazoleamides with ketimines. This protocol discloses efficient access to synthesize a series of spirooxindole-based β-lactams in good to excellent yields and the diastereoselectivity is switchable by tuning the substituents on the α-diazo pyrazoleamides.

Asymmetric Acyclic 1,3-Difunctionalization of Vinyl Carbenes via Site-Selective Vinylogous Mannich-Type Interception of Oxonium Ylides

A novel and highly stereoselective acyclic 1,3-difunctionalization of vinyl metal carbene species has been developed via Rh(II)/chiral phosphoric acid co-catalyzed three-component reactions of vinyldiazoacetates with alcohols and imines. This innovative approach features excellent regio-, diastereo-, and enantioselectivities, demonstrating a broad scope and functional group compatibility. Notably, this is the first example of three-component asymmetric acyclic 1,3-difunctionalization with in situ-formed vinyl metal carbenes.

Brønsted Acid Catalyzed Oxocarbenium-Olefin Metathesis/Rearrangements of 1H-Isochromene Acetals with Vinyl Diazo Compounds

An oxocarbenium-olefin cross metathesis occurs during Brønsted acid catalyzed reactions of 1H-isochromene acetals with vinyl diazo compounds. Formally a carbonyl-alkene [2 + 2]-cyclization between isobenzopyrylium ions and the vinyl group of vinyl diazoesters, the retro-[2 + 2] cycloaddition produces a tethered alkene and a vinyl diazonium ion that, upon loss of dinitrogen, undergoes a highly selective carbocationic cascade rearrangements to diverse products whose formation is controlled by reactant substituents. Polysubstituted benzobicyclo[3.3.1]oxocines, benzobicyclo[3.2.2]oxepines, benzobicyclopropane, and naphthalenes are obtained in good to excellent yields and selectivities. Furthermore, isotopic tracer and control experiments shed light on the oxocarbenium-olefin metathesis/rearrangement process as well as on the origin of the interesting substituent-dependent selectivity.

Enantioselective Formal Vinylogous N-H Insertion of Secondary Aliphatic Amines Catalyzed by a High-Spin Cobalt(II) Complex

Vinylcarbene insertion into the nitrogen-hydrogen (N-H) bond of amines allows direct access to α,β-unsaturated γ-amino acid derivatives, meeting a marked challenge in the control of regio- and enantioselectivities. Here, we report a highly γ-selective and enantioselective insertion into N-H bonds of aliphatic or aromatic secondary amines with vinyl substituted α-diazo pyrazoleamides using a high-spin chiral N,N'-dioxide/cobalt(II) complex catalyst. The method affords a wide variety of valuable optically active Z- and E-type vinyl γ-amino amides. Calculation reveals a spin state change from the quartet cobalt(II) complex to a doublet Co(II)-carbene species for facile Z-selective and enantioselective nucleophilic addition.

Comparison of 1,2-Diarylcyclopropanecarboxylates with 1,2,2-Triarylcyclopropanecarboxylates as Chiral Ligands for Dirhodium-Catalyzed Cyclopropanation and C-H Functionalization

Dirhodium triarylcyclopropanecarboxylate catalysts (Rh₂TPCP₄) are sterically demanding and capable of controlling the site selectivity of C-H functionalization by means of C-H insertion with donor/acceptor carbenes. This study compares the structures and reactivity profiles of dirhodium triarylcyclopropanecarboxylates with dirhodium diarylcyclopropanecarboxylates. The absence of the third aryl group makes the catalysts less sterically demanding and lacks a well-defined preferred conformation. The catalysts have a greater tendency for inducing C-H functionalization at tertiary C-H bonds versus their triaryl counterparts but are generally not capable of achieving high levels of asymmetric induction. These studies confirm the critical requirement of having at least three substituents on the cyclopropanecarboxylate ligands to have well-defined sterically demanding catalysts capable of high levels of asymmetric induction.