Diastereoselectivity Control in Formal Nucleophilic Substitution of Bromocyclopropanes with Oxygen- and Sulfur-Based Nucleophiles

Preparation of Chiral Enantioenriched Densely Substituted Cyclopropyl Azoles, Amines, and Ethers via Formal SN2′ Substitution of Bromocylopropanes

Enantiomerically enriched cyclopropyl ethers, amines, and cyclopropylazole derivatives possessing three stereogenic carbon atoms in a small cycle are obtained via the diastereoselective, formal nucleophilic substitution of chiral, non-racemic bromocyclopropanes. The key feature of this methodology is the utilization of the chiral center of the cyclopropene intermediate, which governs the configuration of the two adjacent stereocenters that are successively installed via 1,4-addition/epimerization sequence.

Facile assembly of 1,5-diazocan-2-ones via cyclization of tethered sulfonamides to cyclopropenes

The sulfonamide moiety was evaluated as an activating and stabilizing functional group in the metal-templated strain release-driven intramolecular nucleophilic addition of amines to cyclopropenes to generate 1,5-diazocan-2-ones.

Organo or Metal Complex Catalyzed Synthesis of Five-membered Oxygen Heterocycles

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The reactions involving the formation of C-O bond using metal as a catalyst have emerged to be one of the most influential reactions for the synthesis of heterocycles in modern organic chemistry. Catalysis by metals offers diverse opportunities to invent new organic reactions with a promising range of selectivities such as chemoselectivity, regioselectivity, diastereoselectivity, and enantioselectivity. The methodologies used earlier for synthesis were less approachable to the organic chemist because of their high cost, highly specified instrumentation and inconvenient methods. For both stereoselective and regioselective formation of five-membered O-containing heterocycles, cyclic reactions that are metal and non-metal-catalyzed have known to be very efficient. The present review article covers the applications of metal and non-metal as a catalyst for the synthesis of five-membered O-containing heterocycles.

Synthesis of aryl cyclopropyl sulfides through copper-promoted S-cyclopropylation of thiophenols using cyclopropylboronic acid

The copper-promoted S-cyclopropylation of thiophenols using cyclopropylboronic acid is reported. The procedure operates under simple conditions to afford the corresponding aryl cyclopropyl sulfides in moderate to excellent yields. The reaction tolerates substitution in ortho-, meta- and para-substitution as well as electron-donating and electron-withdrawing groups. The S-cyclopropylation of a thiophenol was also accomplished using potassium cyclopropyl trifluoroborate.

Metal-Templated Assembly of Cyclopropane-Fused Diazepanones and Diazecanones via exo- trig Nucleophilic Cyclization of Cyclopropenes with Tethered Carbamates

A strain-release-driven, cation-templated nucleophilic 7- and 8- exo-trig-cyclization of tethered Boc-protected amines to cyclopropenes is described. The featured reaction proceeds in diastereo- and regioselective fashion and allows for preparation of the corresponding 2,5-diazabicyclo[5.1.0]octan-6-ones and 2,6-diazabicyclo[6.1.0]nonan-7-ones as sole products in high yields. Preliminary studies on anticancer activities of these novel cyclopropane-fused medium heterocycles were performed.

Directed Cu(I)-Catalyzed Carbomagnesiation of 1-Arylcycloprop-2-ene-1-carboxamides En Route to Densely Substituted Functionalized Cyclopropanes

Copper-catalyzed, directed addition of Grignard reagents across the strained C═C bond of cyclopropene-3-carboxamides was developed. It was demonstrated that the amide functionality serves as an ultimate directing group allowing for highly efficient control of diastereoselectivity of addition including stereoselectivity of electrophilic trapping with prochiral aldehydes. Also, regioselectivity of carbomagnesiation of cyclopropenes with a monosubstituted double bond is investigated. It was shown that in many cases this selectivity is controlled by steric factors and allows for preparation of products with a "reversed" regiochemistry.

Intramolecular nucleophilic addition of carbanions generated from N-benzylamides to cyclopropenes

An unusual reaction is described, involving a formal intramolecular nucleophilic substitution of bromocyclopropanes with nitrogen ylides generated in situ from N-benzyl carboxamides. It is shown that this reaction involves cyclopropene intermediates and allows for the facile and expeditious preparation of 3-azabicyclo[3.1.0]hexan-2-one scaffolds.

Directed nucleophilic addition of phenoxides to cyclopropenes

The alkali metal-templated addition of aryloxides across the double bond of non-conjugated cyclopropenes is described. High cis-selectivity is achieved through a directing effect of a strategically positioned carboxamide functionality.

Efficient one-pot synthesis of 1-arylcycloprop-2-ene-1-carboxamides

An expeditious and cost-efficient method for synthesis of 1-arylcycloprop-2-ene-1-carboxamides was developed. This one-pot protocol involving coupling of amines with acyl chlorides, generated upon treatment of cyclopenylcarboxylic acids with oxalyl chloride, is applicable for the preparation of sensitive products with a reactive, unsubstituted strained double bond.

Templated assembly of medium cyclic ethers via exo-trig nucleophilic cyclization of cyclopropenes

A novel method for the assembly of medium heterocycles via an intramolecular nucleophilic addition to cyclopropenes is described. The exo-trig nucleophilic cyclizations were shown to proceed very efficiently and in a highly diastereoselective fashion affording cis-fused bicyclic products possessing 7 to 10-membered medium rings; starting from a diastereomeric mixtures of bromocyclopropanes.

Synthesis of 1,5-Dioxocanes via the Two-Fold C-O Bond Forming Nucleophilic 4+4-Cyclodimerization of Cycloprop-2-en-1-ylmethanols

An efficient [4+4] cyclodimerization of cyclopropenemethanols operating via a two-fold strain release-driven addition of alkoxides across the double bond of cyclopropenes was investigated. This chemo- and diastereoselective transformation provided previously unknown 2,7-dioxatricyclo[7.1.0.0^4,6]decane scaffolds.

One-pot synthesis of GABA amides via the nucleophilic addition of amines to 3,3-disubstituted cyclopropenes

A one-pot synthesis of various GABA amides has been demostrated, employing the nucleophilic addition of primary and secondary amines across the double bond of cyclopropene-3-carboxamides, followed by ring-opening of the resulting donor-acceptor cyclopropanes and subsequent in situ reduction of enamine (imine) intermediates.

Reaction of cyclopropenes with a trichloromethyl radical: unprecedented ring-opening reaction of cyclopropanes with migration

The triethylborane-mediated direct addition of chloroform to cyclopropenes afforded trichloromethylcyclopropanes. In contrast, the use of dimethylzinc gave the unconjugated diene via ring-opening reactions.

Facially selective Cu-catalyzed carbozincation of cyclopropenes using arylzinc reagents formed by sequential I/Mg/Zn exchange

Described is a Cu-catalyzed directed carbozincation of cyclopropenes with organozinc reagents prepared by I/Mg/Zn exchange. This protocol broadens the scope with respect to functional group tolerance and enables use of aryl iodide precursors, rather than purified diorganozinc precursors. Critical to diastereoselectivity of the carbozincation step is the removal of magnesium halide salts after transmetalation with ZnCl(2).