Enantioselective Friedel–Crafts Alkylation Reactions of β‐Naphthols with Donor–Acceptor Aminocyclopropanes

Merging Two Strained Carbocycles: Lewis Acid Catalyzed Remote Site-Selective Friedel-Crafts Alkylation of in Situ Generated β-Naphthol

Lewis acid catalyzed tandem activation of the two smallest carbocycles, 3-ethoxy cyclobutanones, and donor-acceptor cyclopropanes has been demonstrated. The diphenyl-substituted 3-ethoxy cyclobutanone rearranges itself by intramolecular cyclization for the in situ generation of 1-phenyl 2-naphthol, which further undergoes remote site-selective Friedel-Crafts alkylation with donor-acceptor cyclopropane to synthesize a series of γ-naphthyl butyric acid derivatives. Further control experiments for mechanistic investigations and synthetic applications have also been carried out.

Divergent Copper-salt-controlled Reactions of Donor-Acceptor Cyclopropanes and N-Fluorobenzene Sulfonimide: Access to the 1,3-Haloamines and Aminoindanes

We herein report a method for divergent copper salt controlled reactions of donor-acceptor cyclopropanes and N-fluorobenzene sulfonimide (NFSI). Specifically, in the presence of CuX₂ (X=Cl, Br), the cyclopropanes underwent formal umpolung 1,3-aminohalogenation bifunctionalization via a free radical mediated ring-opening process to afford 1,3-aminochlorination and 1,3-aminobromination products in moderate to good yields. In addition, by using CuI as a catalyst, we synthesized various aminoindane derivatives via 1,3-aminoarylation cyclization of D-A cyclopropanes, the reactions involved a free radical mediated ring-opening and subsequent ring expansion via C-H bond activation.

Ambident reactivity of 5-aminopyrazoles towards donor-acceptor cyclopropanes

Lewis acid-catalysed reactions of donor-acceptor cyclopropanes with 1,3-disubstituted 5-aminopyrazoles were investigated. Under catalysis with gallium(III) chloride, products of the three-membered ring opening via a nucleophilic attack of the exocyclic amino group were obtained in a chemoselective manner. Oppositely, in the presence of scandium(III) triflate, products of either N-alkylation or C(4)-alkylation, or a mixture of both were formed. The products of the C(4) alkylation were transformed in one step into tetrahydropyrazolo[3,4-b]azepines that are attractive for medicinal chemistry and pharmacology.

MgI2-Catalyzed Nucleophilic Ring-Opening Reactions of Donor-Acceptor Cyclopropanes with Indoline-2-thiones

MgI₂-catalyzed nucleophilic ring-opening reactions of donor-acceptor cyclopropanes with indoline-2-thiones as easy-to-handle sulfur nucleophiles were investigated. A series of functionalized γ-indolylthio butyric acid derivatives were synthesized in good to excellent yields under mild reaction conditions. Furthermore, the thioether functionalized ring-opening products could be transformed to sulfone and methionine analogues.

Further Developments and Applications of Oxazoline-Containing Ligands in Asymmetric Catalysis

The chiral oxazoline motif is present in many ligands that have been extensively applied in a series of important metal-catalyzed enantioselective reactions. This Review aims to provide a comprehensive overview of the most significant applications of oxazoline-containing ligands reported in the literature starting from 2009 until the end of 2018. The ligands are classified not by the reaction to which their metal complexes have been applied but by the nature of the denticity, chirality, and donor atoms involved. As a result, the continued development of ligand architectural design from mono(oxazolines), to bis(oxazolines), to tris(oxazolines) and tetra(oxazolines) and variations thereof can be more easily monitored by the reader. In addition, the key transition states of selected asymmetric transformations will be given to illustrate the features that give rise to high levels of asymmetric induction. As a further aid to the reader, we summarize the majority of schemes with representative examples that highlight the variation in % yields and % ees for carefully selected substrates. This Review should be of particular interest to the experts in the field but also serve as a useful starting point to new researchers in this area. It is hoped that this Review will stimulate both the development/design of new ligands and their applications in novel metal-catalyzed asymmetric transformations.

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.

Ring-opening cyclization of spirocyclopropanes with stabilized sulfonium ylides for the construction of a chromane skeleton

Regioselective ring-opening cyclization of cyclohexane-1,3-dione-2-spirocyclopropanes with stabilized sulfonium ylides provided 2,3-trans-disubstituted 2,3,4,6,7,8-hexahydro-5H-1-benzopyran-5-ones in high yields without the formation of any isomers. The obtained product was readily converted into highly substituted chromane.

Expanding the Reactivity of Donor-Acceptor Cyclopropanes: Synthesis of Benzannulated Five-Membered Heterocycles via Intramolecular Attack of a Pendant Nucleophilic Group

Lewis-acid-induced domino transformations of donor-acceptor cyclopropanes, possessing a nucleophilic center embedded in a donor group, into functionalized 2,3-dihydrobenzo[ b]furans and 2,3-dihydrobenzo[ b]thiophenes are reported herein. An unusual switch of the electrophilic center in the three-membered ring, from the atom bearing a donor substituent to an unsubstituted carbon atom, was achieved by a judicious choice of Lewis acid, which induces the isomerization of a cyclopropane to an electrophilic alkene, and the length of linker, connecting a nucleophilic moiety and the small ring.