Cyclopropanes, one of the most important strained rings, have gained much attention for more than a century because of their interesting and unique reactivity They not only exist in many natural products, but have also been widely used in the fields of organic synthesis, medicinal chemistry and materials science as versatile building blocks Based on the sustainable development in this area, this review mainly focuses on the recent advances in the synthesis of cyclopropanes classified by the type of catalytic system, including regio-, diastereo-, and enantio-selective reactions

Recent advances in the synthesis of cyclopropanes

2-Propargyl Alcohols in Organic Synthesis

Just as periscopes allow a submarine to visually search for objects above the surface of the sea, in a reversed periscope fashion electrospray mass spectrometry (ESI-MS) can analyze the compounds at the gas phase/liquid phase interface for chemical entities which may exist in solution. The challenge is the identification and structural characterization of key elusive reaction intermediates in chemical transformations, intermediates which are able to explain how chemical processes occur. This Minireview summarizes recent selected publications on the use of ESI-MS techniques for studying solution intermediates of homogeneous chemical reactions.

Elusive Reaction Intermediates in Solution Explored by ESI-MS: Reverse Periscope for Mechanistic Investigations.

A highly efficient asymmetric cascade reaction between alkynyl esters and allylic alcohols has been realized. Key to success was the combination of a hydroalkoxylation reaction catalyzed by a π-acidic gold(I) complex with a Claisen rearrangement catalyzed by a chiral Lewis acidic N,N′-dioxide–nickel(II) complex. A range of acyclic α-allyl β-keto esters were synthesized in high yields (up to 99 %) with good diastereoselectivities (up to 97:3) and excellent enantioselectivities (up to 99 % ee) under mild reaction conditions. These products can be easily transformed into optically active β-hydroxy esters, β-hydroxy acids, or 1,3-diols.

Gold(I)/Chiral N,N'-Dioxide-Nickel(II) Relay Catalysis for Asymmetric Tandem Intermolecular Hydroalkoxylation/Claisen Rearrangement.

Recent developments in cyclopropene chemistry

Metallacycle-Mediated Cross-Coupling in Natural Product Synthesis.

The conjugate addition of an alcohol to a butynoate ester using an organophosphine catalyst was monitored using pressurized sample infusion electrospray ionization mass spectrometry (PSI-ESI-MS), together with 31P and 1H NMR spectroscopy. The combination of methods allowed examination of the reaction progress from the perspective of reactants and products (1H NMR) and insights into behaviors of the reaction intermediates and formation of byproducts (31P NMR and MS). The resulting traces could be closely approximated through numerical modeling by appropriate selection of rate constants, and a sound understanding of the mechanism and the means by which oligomeric byproducts are formed allows a rational approach to experimental design.

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A multi-pronged mechanistic study of the phosphine-mediated conjugate addition of an alcohol to an acetylenic ester

We recently described an iterative synthesis of oligo-vinyl ethers, followed by a radical cascade to provide a family of hexahydro-2H-furo[3,4-b]pyrans. Our results for the radical cascade were consistent with either a direct 6-endo-trig addition of a vinyl radical onto the first vinyl ether function or an initial 5-exo-trig addition, followed by rearrangement to the more stable anomeric radical intermediate. In this report, we describe our further mechanistic studies aimed at distinguishing between these two possibilities and conclude that the 5-exo/3-exo/retro-3-exo pathway is dominant.

Cascading radical cyclization of bis-vinyl ethers: mechanistic investigation reveals a 5-exo/3-exo/retro-3-exo/5-exo pathway.

ISX-9 can potentiate cell proliferation and neuronal commitment in the rat dentate gyrus

Kinetic investigations of substituent effects in the thermal rearrangement of bis-vinyl ether substrates are reported. Findings indicate that the influence of the various substituent patterns on the rate of rearrangement in these compounds differs from that documented in the literature for the analogous [3,3]-sigmatropic rearrangement of allyl vinyl ethers. In addition, the thermochemical data collected suggests the existence of a dissociative transition state with significant dipolar character. These findings provide a unique contribution to the already extensive body of literature dedicated to mechanistic investigation of the Claisen rearrangement of aliphatic allyl vinyl ethers.

Investigation of quantitative structure–reactivity relationships in the aliphatic Claisen rearrangement of bis-vinyl ethers reveals a dipolar, dissociative mechanism

Natasha F. O’Rourke

Papers

Metallacycle-Mediated Cross-Coupling in Natural Product Synthesis.

A multi-pronged mechanistic study of the phosphine-mediated conjugate addition of an alcohol to an acetylenic ester

Cascading radical cyclization of bis-vinyl ethers: mechanistic investigation reveals a 5-exo/3-exo/retro-3-exo/5-exo pathway.

ISX-9 can potentiate cell proliferation and neuronal commitment in the rat dentate gyrus

Investigation of quantitative structure–reactivity relationships in the aliphatic Claisen rearrangement of bis-vinyl ethers reveals a dipolar, dissociative mechanism