Ring Opening of Donor-Acceptor Cyclopropanes with Acyclic 1,3-Diketones for the Synthesis of 1,6-Dicarbonyl Compounds

Synthesis of Unsymmetrical 1,6-Dicarbonyl Compounds through Photocatalytic One-Pot Tandem Three-Component Reaction

Unsymmetrical 1,6-dicarbonyl compounds are useful building blocks in organic synthesis. However, the synthetic methods are limited. Herein we report a three-component one-pot reaction for the synthesis of unsymmetrical 1,6-diketones. This reaction utilizes sulfides as radical precursors and enol ethers as building blocks. It takes advantage of photocatalysis and Lewis acid catalysis. Its synthetic utility was demonstrated in the modification of biorelevant compounds.

A visible light-driven direct synthesis of industrially relevant glutaric acid diesters from aldehydes

A straightforward and practical method has been developed to access α-substituted glutaric diesters from acrylates and aldehydes using visible light, with Eosin Y facilitating hydrogen atom transfer (HAT) and subsequent Giese-type addition. Also, sunlight has been successfully used as an alternative sustainable light source. The method has also been explored to access substituted 4,5-dihydro-2H-pyridazinones, which have potential biological and industrial applications. Comprehensive mechanistic investigations have been carried out.

Asymmetric ring-opening reactions of donor-acceptor cyclopropanes with 1,3-cyclodiones

Asymmetric ring-opening reactions of donor-acceptor cyclopropanes with 1,3-cyclodiones have been established for the synthesis of enantioenriched γ-hydroxybutyric acid derivatives in the presence of Cu(ii)/trisoxazoline catalyst. These reactions offered the desired products in 70% to 93% yields with 79% to 99% enantiomeric excesses.

Metal-Free Regioselective Hydrophosphorodithioation of Spirovinylcyclopropyl Oxindoles: Rapid Access to Allyl Dialkylphosphorodithioates

Phosphorodithioates are important substructures due to their great use in bioactive compounds and functional materials. A metal-free 1,5-addition of spirovinylcyclopropyl oxindoles have been developed by choosing P₄S₁₀ and alcohol as nucleophiles through the regioselective ring-opening of spirovinylcyclopropyl oxindoles. This method provides access to allylic organothiophosphates with high efficiency, wide functional group tolerance, good chemo- and regioselectivity, and E-selectivity. 1,3-Addition products were also prepared in high yield. Furthermore, the resulting organothiophosphates could be readily transformed into other allylic derivatives.

Ambident reactivity of 5-aminopyrazoles towards donor-acceptor cyclopropanes

Lewis acid-catalysed reactions of donor-acceptor cyclopropanes with 1,3-disubstituted 5-aminopyrazoles were investigated. Under catalysis with gallium(III) chloride, products of the three-membered ring opening via a nucleophilic attack of the exocyclic amino group were obtained in a chemoselective manner. Oppositely, in the presence of scandium(III) triflate, products of either N-alkylation or C(4)-alkylation, or a mixture of both were formed. The products of the C(4) alkylation were transformed in one step into tetrahydropyrazolo[3,4-b]azepines that are attractive for medicinal chemistry and pharmacology.

MgI2-Catalyzed Nucleophilic Ring-Opening Reactions of Donor-Acceptor Cyclopropanes with Indoline-2-thiones

MgI₂-catalyzed nucleophilic ring-opening reactions of donor-acceptor cyclopropanes with indoline-2-thiones as easy-to-handle sulfur nucleophiles were investigated. A series of functionalized γ-indolylthio butyric acid derivatives were synthesized in good to excellent yields under mild reaction conditions. Furthermore, the thioether functionalized ring-opening products could be transformed to sulfone and methionine analogues.

Lewis acid-catalyzed [3 + 2] annulations of oxindole based spirocyclic donor-acceptor cyclopropanes with ynamides

[3 + 2] annulations of oxindole based spirocyclic donor-acceptor cyclopropanes and ynamides catalyzed by copper triflate have been developed for the synthesis of biologically important spirocyclopenteneoxindoles. These reactions tolerated a wide scope of substrates and provided the desired products in good to high yields (up to 90%) with up to >40 : 1 diastereoselectivities under mild conditions.

Stereoselective tandem iridium-catalyzed alkene isomerization-cope rearrangement of ω-diene epoxides: efficient access to acyclic 1,6-dicarbonyl compounds

The Cope rearrangement of 2,3-divinyloxiranes, a rare example of epoxide C-C bond cleavage, results in 4,5-dihydrooxepines which are amenable to hydrolysis, furnishing 1,6-dicarbonyl compounds containing two contiguous stereocenters at the 3- and 4-positions. We employ an Ir-based alkene isomerization catalyst to form the reactive 2,3-divinyloxirane in situ with complete regio- and stereocontrol, which translates into excellent control over the stereochemistry of the resulting oxepines and ultimately to an attractive strategy towards 1,6-dicarbonyl compounds.

Protic Ionic Liquid as Reagent, Catalyst, and Solvent: 1-Methylimidazolium Thiocyanate

We propose a new concept of the triple role of protic ionic liquids with nucleophilic anions: a) a regenerable solvent, b) a Brønsted acid inducing diverse transformations via general acid catalysis, and c) a source of a nucleophile. The efficiency of this strategy was demonstrated using thiocyanate-based protic ionic liquids for the ring-opening of donor-acceptor cyclopropanes. A wide variety of activated cyclopropanes were found to react with 1-methylimidazolium thiocyanate under mild metal-free conditions via unusual nitrogen attack of the ambident thiocyanate ion on the electrophilic center of the three-membered ring affording pyrrolidine-2-thiones bearing donor and acceptor substituents at the C(5) and C(3) atoms, respectively, in a single time-efficient step. The ability of 1-methylimidazolium thiocyanate to serve as a triplex reagent was exemplarily illustrated by (4+2)-annulation with 1-acyl-2-(2-hydroxyphenyl)cyclopropane, epoxide ring-opening and other organic transformations.