Epoxides: Small Rings to Play with under Asymmetric Organocatalysis

Abstract

Optically pure epoxides are recognized as highly valuable products and key intermediates, useful in different areas from pharmaceutical and agrochemical industries to natural product synthesis and materials science. The predictable fate of the ringopening process, in terms of stereoselectivity and often of regioselectivity, enables useful functional groups to be installed at vicinal carbon atoms in a desired manner. In this way, products of widespread utility either for synthetic applications or as final products can be obtained. The advent of asymmetric organocatalysis provided a new convenient tool, not only for their preparation but also for the elaboration of this class of heterocycles. In this review, we focus on recent developments of stereoselective organocatalytic ringopening reactions of meso-epoxides, kinetic resolution of racemic epoxides, and Meinwald-type rearrangement. Examples of asymmetric organocatalytic processes toward specific synthetic targets, which include ring opening of an epoxide intermediate, are also illustrated.

Convenient Synthesis of N-Heterocycle-Fused Tetrahydro-1,4-diazepinones

“…According to the synthetic strategy, ethyl 1-(oxiran-2-ylmethyl)-3-aryl-1H-pyrazole-5carboxylates 2a-h were further used to obtain novel fused pyrazole-diazepinone systems via oxirane ring-opening. Due to high ring-strain, epoxides are prone to undergoing ringopening reactions upon treatment with various nucleophiles [55] alone, or under the use of transition metal or organocatalysts [56][57][58]. On the other side, small heterocycles are also able to react with diverse electrophiles, affording a variety of functionalized molecules.…”

Metal‐Free Ring‐Opening of Epoxides

“…[28][29][30][31] In 2011 Vacarro et al [32] published a review on the nucleophilic ring opening of 1,2-epoxides in water which highlighted the combined catalytic effects of epoxide properties and water as a consequence of its physical properties, pH of the reaction medium. In the recent past, research groups of Yadav, [11] Wang [12] and Lattanzi [13,14] reviewed developments in organocatalyzed enantioselective asymmetric ring opening reactions of 1,2-epoxides and desymmetrization of meso-epoxides independently but limited nucleophiles and epoxide substrate scope.Our group has been working in this field since 2008 and we have reported for the first time peptide based thiourea organocatalyst for the asymmetric ring opening of meso-epoxide with amines. [33] In continuation of this work, we have compiled here the literature reports from the past two decade forthe development of various metal free methodologies and catalytic systems including a wide range of epoxide substrates and nucleophiles for the ring opening of epoxides, which will help the new researchers to develop a better understanding of the the concept.…”

“…Consequently, synthetic chemists have directed considerable attention to the development of synthetic methods using ring opening of epoxides in order to procure1,2-disubstituted functionalized products having advanced pharmaceutical values. [11][12][13][14][15][16] Literature contains number of reports on chiral as well as achiral ring opening of epoxides but most of these reports include the use of Lewis acid as catalysts. [17,18] The Lewis acid catalyzed reactions have some serious disadvantages such as use of hazardous solvents, high cost of metal catalysts, tedious workup, inert reaction conditions, side reactions, use of morethan equivalent amounts and sometimes very low catalytic turnover etc.…”

Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study

“…Epoxides (also known as oxiranes) are classes of compounds with two carbon atoms connected to an oxygen atom forming a three-membered ring (3MR). Due to the ring strain and polarization of the C-O bonds in the 3MR, the epoxide group is highly reactive, making epoxides valuable chemical intermediates stretching from organic synthesis and catalysis [1][2][3][4][5], the design of polymers and materials, e.g., based on natural terpene epoxides [6] to their use as raw materials in various industries producing fine chemicals for pharmaceuticals, fragrances, food or other agricultural products [7][8][9][10][11][12][13][14][15][16]. Ethylene oxide and propylene oxide are among the highest volume products in our industry, with annual production rates of 15 and 3 Mt per year, respectively [1].…”

“…Optically enriched epoxides are important heterocyclic intermediates for enantioselective synthesis [27][28][29], including natural and bioactive products [2,30], or agrochemicals, such as fungicides, herbicides, insecticides and pheromones [8]. A pure enantiomeric product is even more important in pharmaceutical industry, where high enantiomeric excess is needed due to the different physiological effects that one enantiomer can show after interacting with a chiral biological target [14,16,[31][32][33][34].…”