Catalytic [3 + 2] Cycloaddition through Ring Cleavage of Simple Cyclopropanes with Isocyanates

Recent updates on vinyl cyclopropanes, aziridines and oxiranes: access to heterocyclic scaffolds

This present review delineates the repertoire of vinyl cyclopropanes and their stuctural analogues to accomplish a wide array of oxa-cycles, aza-cycles, and thia-cycles under transition metal catalysis and metal-free approaches from early 2019 to the present date. The generation of electrophilic π-allyl intermediates and 1-3/1-5-dipolarophile chemistry originating from VCPs are always green, step- and atom-economical and sustainable strategies in comparsion with prefunctionalized and/or C-H activation protocols. Here, the strained ring-system extends its applicability by relieving the strain to undergo a ring-expansion reaction to accomplish 5-9 membered carbo- and heterocyclic systems. The availability of chiral ligands in the ring-expansion reaction of VCPs and their analogues has paved the way to realizing asymmetric synthetic transformations.

Chemoselective Ullmann Reaction of α-Trisubstituted Thioamides: Synthesis of Novel 2-Iminobenzothiolanes

New classes of unexplored benzo[b]thiolanes are synthesized from trisubstituted thioamides through copper-catalyzed intramolecular S-arylation of thioamides for the first time. This method provides good to excellent yields with fully controlled chemoselectivity. Unusually, iminobenzo[b]thiolanes are very stable under mild acidic conditions. A plausible mechanism is proposed for the chemoselective S-arylation process.

Direct use of 1,3-dienes for the allylation of ketones via catalytic hydroindation

In this study, in situ catalytically generated allylic indium from 1,3 dienes and InCl₂H was developed for use in the allylation of ketones.

Palladium-catalysed ring-opening [3 + 2]-annulation of spirovinylcyclopropyl oxindole to diastereoselectively access spirooxindoles

A novel palladium-catalysed ring-opening [3 + 2]-annulation of spirovinylcyclopropyl oxindole with α,β-unsaturated nitroalkenes is reported. A series of spirooxindole derivatives were synthesized in high yields and good to excellent diastereoselectivities. This developed protocol offers a new and efficient pathway for the assembly of spirooxindoles.

Ni-Al Bimetallic Catalyzed Enantioselective Cycloaddition of Cyclopropyl Carboxamide with Alkyne

A Ni-Al bimetallic catalyzed enantioselective cycloaddition reaction of cyclopropyl carboxamides with alkynes has been developed. A series of cyclopentenyl carboxamides were obtained in up to 99% yield and 94% ee. The bifunctional-ligand-enabled bimetallic catalysis proved to be an efficient strategy for the C-C bond cleavage of unreactive cyclopropanes.

Catalytic Annulation of Diethyl Methylenecyclopropane-1,1-dicarboxylate with 1,1-Dicyanoalkenes

The catalytic annulation of methylenecyclopropane 1 with 1,1-dicyanoalkenes 2 using a Mg-Sn catalytic system was developed. Selective formation of cyclopentylidenemalonates 3 and spiro[2,3]hexane-1,1-dicarboxylates 4 was accomplished via the choice of a proper solvent and an effective catalytic system.

Diastereoselective Synthesis of Spirocyclopropanes under Mild Conditions via Formal [2 + 1] Cycloadditions Using 2,3-Dioxo-4-benzylidene-pyrrolidines

A highly diastereoselective cyclopropanation of cyclic enones with sulfur ylides was developed under catalyst-free conditions, producing multifunctional spirocyclopropanes in generally excellent yields (up to 99% yield and >99:1 d.r.). The asymmetric version of this method was realized by using an easily available chiral sulfur ylide, affording products with moderate to good stereoselectivity.

Diastereoselective Intramolecular [3 + 2]-Annulation of Donor-Acceptor Cyclopropane with Imine-Assembling Hexahydropyrrolo[3,2-c]quinolinone Scaffolds

An intramolecular [3 + 2]-annulation of amide-linked donor-acceptor cyclopropane with in situ-generated imine is described. As a result, diverse hexahydropyrrolo[3,2-c]quinolinones, as the tricyclic core of martinellines, were efficiently assembled in good to excellent yield (up to 93%) with a good diastereomeric ratio (up to 98:2).

Efficient Benzimidazolidinone Synthesis via Rhodium-Catalyzed Double-Decarbonylative C-C Activation/Cycloaddition between Isatins and Isocyanates

The first decarbonylative cycloaddition of less-strained cyclic ketones (isatins) with isocyanates is reported. Initiated by C-C activation, this distinct [5-2+2] transformation provides a rapid entry to access various benzimidazolidinone derivatives, through which a wide range of isocyanates can be efficiently coupled with broad functional group tolerance. A modified one-pot process, combining Curtius rearrangement and C-C activation, was also achieved by using acyl azides as the starting materials. Detailed mechanistic study revealed a surprising double-decarbonylative reaction pathway. The novel reactivity discovered in this basic research is expected to shed light on developing new heterocycle formation methods through a C-C/isocyanate coupling.