Acetic Acid Mediated Regioselective [3 + 3] Cycloaddition of Substituted Cyclopropane-1,1-dicarbonitriles with 1,4-Dithiane-2,5-diol

An acetic acid mediated regioselective [3 + 3] cycloaddition of substituted cyclopropane-1,1-dicarbonitriles with in situ generated mercaptoacetaldehyde was developed for the synthesis of highly stereoselective tetrahydrothiopyranols. This transformation created two new bonds in a single operation for generating complexity in tetrahydrothiopyrans. This method is characterized by cheap and readily available starting materials, simple operation, and mild reaction conditions.

Yb(OTf)3-Mediated Annulation of Cyclopropane-1,1-dicarbonitriles with 2-Aminobenzaldehydes for Synthesis of Polysubstituted Quinolines

A Yb(OTf)₃-mediated annulation of cyclopropane-1,1-dicarbonitriles and 2-aminobenzaldehydes for the synthesis of polysubstituted quinolines in generally good yields was investigated. In the cascade reaction, the protocol includes ring opening, intermolecular nuclophilic addition, intramolecular nuclophilic addition, and demalononitrile aromatization, in which the malononitrile group serves as a deciduous directing group mediated by Yb(OTf)₃.

Recent advances in ring-opening of donor acceptor cyclopropanes using C-nucleophiles

Ring-opening transformations of donor-acceptor cyclopropanes (DAC) with carbon-centered nucleophiles is a simple, straight-forward approach to 1,3-bifunctional compounds that has witnessed remarkable progress over the past several years. To date, different reactivity patterns of DACs have been successfully exploited in racemic/stereoselective syntheses of various acyclic compounds or carbocycles with an impressive structural diversity. The thriving strategies have been successfully utilized in multistep synthesis of complex target molecules. Herein, the recent advances (2015-present) in the ring-opening of DAC involving electron rich arenes and indoles, active methylene compounds, various dipolarophiles, organoborates/boronates, vinyl ethers etc. following Friedel-Crafts alkylation, annulation/formal cycloaddition reaction, organocatalytic reaction, Nazarov cyclisation etc. are presented.

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.

Highly Chemoselective [2+1] Annulation of α-Alkylidene Pyrazolones with α-Bromonitroalkenes: Synthesis of Pyrazolone-Based Vinylcyclopropanes and Computational Studies

A highly chemoselective [2+1] annulation of α-alkylidene pyrazolones with α-bromonitroalkenes has been achieved under mild conditions. α-Alkylidene pyrazolones were unprecedentedly used as a C1 synthon to participate in annulation reactions, providing access to diverse vinylcyclopropane-based pyrazolone products. In addition, a spectrum of pharmaceutically interesting pyrazole-fused pyranone oximes could be rapidly obtained through a [2+1] annulation/rearrangement sequential process. Computational studies disclosed the origin of the observed chemoselectivity of the [2+1] cycloaddition.