Ring-Opening Cyclization of Alkylidenecyclopropyl Ketones with Amines. An Efficient Synthesis of 2,3,4-Trisubstituted Pyrroles

Ruthenium-catalyzed acceptorless dehydrogenative coupling of amino alcohols and ynones to access 3-acylpyrroles

Herein, a new strategy for the direct synthesis of functionalized pyrroles from β-amino alcohols and ynones via ruthenium-catalyzed acceptorless dehydrogenative coupling has been demonstrated. This developed methodology proceeds in an atom- and step-economic fashion together with the merits of broad substrate scope, operational simplicity, and water and hydrogen gas as the sole by-products, which provides an alternative and sustainable way to access functionalized pyrroles. Further, this method was applied to the rapid synthesis of the COX-1/COX-2 inhibitor and boron dipyrromethene derivative successfully.

Thermally-induced intramolecular [2 + 2] cycloaddition of acrylamide-tethered alkylidenecyclopropanes

An efficient and highly regio- and diastereoselective synthetic method to cyclobutane-containing spiro[2.3]hexane fused with six-membered hetero-cycles has been disclosed via a thermally-induced intramolecular [2 + 2] cycloaddition of acrylamide-tethered alkylidenecyclopropanes. The DFT calculations indicate that this intramolecular cycloaddition proceeds in a concerted manner and account for the product selectivity. These reactions exhibited excellent yields and functional group tolerance under metal free conditions.

Heterocycles from methylenecyclopropanes

The discovery of a series of novel organic reactions has made methylenecyclopropanes (MCPs) some of the most popular building blocks in synthetic organic chemistry during the past two decades. Among reported works, the construction of heterocycles from MCPs has highlighted new synthetic methodologies that afford more opportunities for the quick synthesis of elaborately substituted products, and this should draw a great deal of attention. However, reviews in this area are insufficient, and the latest monograph on heterocycle synthesis from MCPs was published 12 years ago. This review aims to summarize the novel organic reactions of MCPs to produce heterocycles published in recent years, which have provided specific and powerful tools for organic synthesis.

β-Cyclodextrin as a recyclable catalyst: aqueous phase one-pot four-component synthesis of polyfunctionalized pyrroles

An elegant, mild and straightforward methodology was explored for the first time towards the synthesis of polyfunctionalized pyrroles using β-cyclodextrin as a reusable supramolecular catalyst in aqueous medium.

Radical–radical cross coupling reactions of photo-excited fluorenones

Radical–radical cross coupling reactions of photoexcited 9-fluorenones have been accomplished for the first time, leading to the synthesis of 9-alkyl, pyrollidinyl and spiro-THF derivatives of 9-fluorenones.

Zn(OTf)2 promoted rearrangement of 1,2-cyclopropanated sugars with amines: a convenient method for the synthesis of 3-polyhydroxyalkyl-substituted pyrrole derivatives

A rearrangement reaction of 1,2-cyclopropanated sugars with alkylamines or arylamines promoted by Zn(OTf)2 is described. The method offers a series of 3-polyhydroxyalkyl-substituted pyrrole derivatives with multiple chiral centers in moderate to excellent yields. The epimerization is achieved by inverting the stereochemistry at the free hydroxyl group of the resulting pyrrole, which would give access to many more possible stereoisomers.

Selective synthesis of 2,5-disubstituted furan-3-carboxylates and the isomeric 2,4-disubstituted furan-3-carboxylates

Regioselective formation of 2,5-disubstituted furan-3-carboxylates and the isomeric 2,4-disubstituted furan-3-carboxylates from the same substrates was realized under different reaction condition.

Catalyst-dependent divergent synthesis of pyrroles from 3-alkynyl imine derivatives: a noncarbonylative and carbonylative approach

A novel Ru(0)- and Rh(I)-catalyzed noncarbonylative and carbonylative cycloisomerization of readily available 3-alkynyl imine derivatives has been developed to provide 3,4-fused or nonfused pyrrole derivatives efficiently in moderate to excellent yields. The key steps involve the formation of a ruthenium carbenoid intermediate or a rhodacycle intermediate, respectively. In these reactions, CO can serve as a ligand or a reagent.

Simple two-step synthesis of 2,4-disubstituted pyrroles and 3,5-disubstituted pyrrole-2-carbonitriles from enones

The cyclocondensation of enones with aminoacetonitrile furnishes 3,4-dihydro-2H-pyrrole-2-carbonitriles which can be readily converted to 2,4-disubstituted pyrroles by microwave-induced dehydrocyanation. Alternatively, oxidation of the intermediates produces 3,5-disubstituted pyrrole-2-carbonitriles.

Stereoselective Rh2(S-IBAZ)4-catalyzed cyclopropanation of alkenes, alkynes, and allenes: asymmetric synthesis of diacceptor cyclopropylphosphonates and alkylidenecyclopropanes

A mild and highly stereoselective rhodium(II)-catalyzed cyclopropanation of alkenes, alkynes, and allenes with diacceptor diazo compounds is reported. Using the phosphonate moiety as an efficient trans-directing group, the first catalytic asymmetric route to diacceptor cycloprop(en)ylphosphonates was developed by employing an α-cyano diazophosphonate and Rh(2)(S-IBAZ)(4) as chiral catalyst. The isosteric character of phosphonic and carboxylic acid derivatives allowed the alternative use of an α-cyano diazo ester in the process, leading to α-cyano cycloprop(en)ylcarboxylates in high yields and stereoselectivities. Taking advantage of the particular reactivity of the cyanocarbene intermediates involved in this system, the scope of compatible substrates could be extended to substituted allenes, leading to the development of the first catalytic enantioselective method for the synthesis of diacceptor alkylidenecyclopropanes.