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

4b,5,6,9-Tetrahydro-7<i>H</i>-dibenzo[<i>c</i>,<i>e</i>]pyrrolo[1,2-<i>a</i>]azepin-7-one

A simple approach to synthesize 4b,5,6,9-tetrahydro-7H-dibenzo[c,e]pyrrolo[1,2-a]azepin- 7-one has been developed, based on a three-step transformation of 2-(2-bromophenyl)cyclopropane-1,1-diester. The key stage in this method is an intramolecular cross-coupling of 1-(2-bromobenzyl)-5-(2-bromophenyl)pyrrolidin-2-one under continuous flow conditions in an H-Сube-Pro using commercially available supported Pd catalysts

Dimethyl 2-{[2-(2-Methoxy-1-methoxycarbonyl-2-oxoethyl)-4,5,7-trimethoxy-3-(2,4,5-trimethoxyphenyl)-2,3-dihydro-1H-inden-1-yl]methyl}malonate

A simple synthetic approach to dimethyl 2-{[2-(2-methoxy-1-methoxycarbonyl-2-oxoethyl)-4,5,7-trimethoxy-3-(2,4,5-trimethoxyphenyl)-2,3-dihydro-1H-inden-1-yl]methyl}malonate has been developed, based on a B(C6F5)3-induced domino dimerization of 2-(2,4,5-trimethoxyphenyl)cyclopropane-1,1-diester

Transformation of 3-(Furan-2-yl)-1,3-di(het)arylpropan-1-ones to Prop-2-en-1-ones via Oxidative Furan Dearomatization/2-Ene-1,4,7-triones Cyclization

The approach to 3-(furan-2-yl)-1,3-di(het)arylprop-2-en-1-ones based on the oxidative dearomatization of 3-(furan-2-yl)-1,3-di(het)arylpropan-1-ones followed by an unusual cyclization of the formed di(het)aryl-substituted 2-ene-1,4,7-triones has been developed. The cyclization step is related to the Paal–Knorr synthesis, but the furan ring formation is accompanied in this case by a formal shift of the double bond through the formation of a fully conjugated 4,7-hydroxy-2,4,6-trien-1-one system or its surrogate

Oxidative Furan-to-Indole Rearrangement. Synthesis of 2‑(2-Acylvinyl)indoles and Flinderole C Analogues

Oxidative rearrangement of 2-(2-aminobenzyl)­furans affording 2-(2-acylvinyl)­indoles in a stereocontrolled manner in good-to-excellent yields has been developed. Thus, (2-aminobenzyl)­furans with electron-releasing alkoxy substituents in the phenyl group form only <i>E</i>-isomers of 2-(2-acylvinyl)­indoles. Conversely, substrates without such substituents produce target products as <i>Z</i>-isomers exclusively. A short diastereoselective method for the transformation of the obtained 2-(2-acylvinyl)­indoles into antimalarial bisindole alkaloid flinderole A–C analogues has been developed

Convenient Synthesis of Functionalized Cyclopropa[c]coumarin-1a-carboxylates

A simple method has been developed for the synthesis of cyclopropa[c]coumarins, which belong to the donor-acceptor cyclopropane family and, therefore, are promising substrates for the preparation of chromene-based fine chemicals. The method, based on the acetic acid-induced intramolecular transesterification of 2-arylcyclopropane-1,1-dicarboxylates, was found to be efficient for substrates containing hydroxy group directly attached to the aromatic ring

Synthesis of (Het)aryl 2-(2-hydroxyaryl)cyclopropyl Ketones

A simple general method for the synthesis of 1-acyl-2-(ortho-hydroxyaryl)cyclopropanes, which belong to the donor&ndash;acceptor cyclopropane family, has been developed. This method, based on the Corey&ndash;Chaykovsky cyclopropanation of 2-hydroxychalcones, allows for the preparation of a large diversity of hydroxy-substituted cyclopropanes, which can serve as promising building blocks for the synthesis of various bioactive compounds

A Simple Route to Polysubstituted Indoles Exploiting Azide Induced Furan Ring Opening

A straightforward, efficient indole synthesis based on thermolysis of 2-(2-azido­benzyl)­furans with attack of the formed nitrene moiety onto the <i>ipso</i> position of furan ring has been developed. The cyclization is accompanied by furan ring opening and affords indoles with a 2-acylvinyl substituent suitable for further modifications

Lewis Acid Triggered Vinylcyclopropane–Cyclopentene Rearrangement

We report a mild Lewis acid induced isomerization of donor–acceptor cyclopropanes, containing an alkenyl moiety and diverse electron-withdrawing group(s) at the adjacent positions, into substituted cyclopentenes. We have found that 1,1,2-trisubstituted cyclopent-3-enes were exclusively obtained in yield of 51–99% when cyclopropanes with a 2-substituted alkenyl group as a donor underwent isomerization. For cyclopropanes bearing a trisubstituted alkenyl group either the corresponding cyclopent-3-enes or isomeric cyclopent-2-enes having two acceptor groups at the C(1) atom were formed, with the reaction selectivity being determined by the applied Lewis acid. We have shown that the reactivity of the donor–acceptor cyclopropane increases with the increase of the electron-donating character of (hetero)­aromatic group attached to the alkenyl moiety. The synthetic utility of the developed methodology was also demonstrated through the synthesis of polysubstituted cyclopentane and piperidine derivatives