Scandium(III) Triflate-Catalyzed Reaction of Aroyl-Substituted Donor-Acceptor Cyclopropanes with 1-Naphthylamines: Access to Dibenzo[c,h]acridines

Cs2CO3-Mediated Annulation of Cyclopropane-1,1-dicarbonitriles with o-Benzenediamines: Access to Substituted 2-Aminoquinoxalines

The Cs2CO3-mediated formal (4 + 2) cascade annulation strategy for the synthesis of 2-aminoquinoxalines has been developed using D-A cyclopropanes and o-benzenediamines as the substrates. The protocol provides an efficient method of accessing a broad range of 2-aminoquinoxaline derivatives in good to excellent yields with good functional-group tolerance.

DABCO-Promoted (3 + 2) Annulation of D-A Cyclopropanes with Alkynoates for the Synthesis of Cyclopentenol Derivatives

Efficient synthesis of highly functionalized cyclopentenols with an exocyclic Z double bond was investigated via a (3 + 2) annulation reaction of 2-aroyl-D-A (donor-acceptor) cyclopropanes with alkynoates in the presence of DABCO. This synthetic approach featured a wide range of readily available 2-aroyl-substituted D-A cyclopropanes with diverse functional groups, densely substituted cyclopentenols with two stereogenic centers and an exocyclic double bond in a highly stereocontrolled manner and had operationally simple and mild reaction conditions.

Synthesis of Fully Substituted Pyrazoles with a Dicyanomethyl Group via DBU/Lewis Acid-Mediated Annulation of D-A Cyclopropanes with Arylhydrazines

The efficient synthesis of fully substituted pyrazoles with a dicyanomethyl group was developed via an annulation reaction of 2-aroyl D-A cyclopropanes with arylhydrazines in the presence of DBU/AlCl3 reaction systems. This synthetic approach featured a wide range of readily available aroyl-substituted D-A cyclopropanes with diverse functional groups and a diversity of substituents on pyrazole products and had operationally simple and mild reaction conditions.

Annulation of 2-Aroyl D-A Cyclopropanes via Selectively Ring-Opening Process with o-Benzenediamines to Access Quinoxaline Derivatives

An annulation reaction of 2-aroyl D-A cyclopropanes with o-benzenediamines via selective cleavage of C-C bonds of cyclopropane in the presence of DBU/Sc(OTf)3 reaction systems was developed for the direct preparation of 2-aryl-3-benzylquinoxalines. This synthetic approach tolerated a wide range of readily available aroyl-substituted D-A cyclopropanes with diverse functional groups and had operationally simple and mild reaction conditions.

Tandem Dearomative/Rearomative (3 + 2) Annulation of Aroyl-Substituted Donor-Acceptor Cyclopropanes with Benzothiazoles

A series of benzo[d]pyrrolo[2,1-b]thiazoles was synthesized by (3 + 2) annulation of aroyl-substituted donor-acceptor cyclopropanes with benzothiazoles. The annulation, promoted by a substoichiometric amount of Sc(OTf)₃, takes place through the formation of the respective dearomatized (3 + 2) adducts, followed by unexpected decarbethoxylative and dehydrogenative rearomatization to afford fully aromatized products. The unusual reactivity is attributed to the presence of an extra aroyl group in the donor-acceptor cyclopropanes.

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.

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.

The Cloke-Wilson rearrangement of aroyl-substituted donor-acceptor cylopropanes containing arylethyl donors

The chemistry of donor-acceptor (D-A) cyclopropanes containing alkyl donors has been scantily investigated. In the present work, we have synthesized new D-A cyclopropanes containing arylethyl donors and explored their reactivity in the presence of Lewis acids. Upon treatment with SnCl₄, these cyclopropanes underwent the Cloke-Wilson rearrangement to yield 3,4,5-trisubstituted γ-butyrolactones in good yields with high diastereoselectivity.

Expanding Stereoelectronic Limits of endo-tet Cyclizations: Synthesis of Benz[b]azepines from Donor-Acceptor Cyclopropanes

The importance of intramolecular constraints in cyclic transition-state geometries is especially pronounced in n-endo-tet cyclizations, where the usual backside approach of a nucleophile to the breaking bond is impossible for the rings containing less than eight atoms. Herein, we expand the limits of endo-tet cyclizations and show that donor-acceptor cyclopropanes can provide a seven-membered ring via a genuine 6-endo-tet process. Substrates containing a N-alkyl-N-arylcarbamoyl moiety as an acceptor group undergo Lewis acid-induced cyclization to form tetrahydrobenz[b]azepin-2-ones in high yields. The reaction proceeds with the inversion of the configuration at the electrophilic carbon. In this process, a formally six-membered transition state yields a seven-membered ring as the pre-existing cycle is merged into the forming ring. The stereochemistry of the products can be controlled by the reaction time and by the nature of Lewis acid, opening access to both diastereomers by tuning of the reaction conditions.

Tin(iv) chloride mediated (3 + 2) annulation of trans-2-aroyl-3-styrylcyclopropane-1,1-dicarboxylates with nitriles: diastereoselective access to 5-vinyl-1-pyrroline derivatives

A tin(iv) chloride promoted (3 + 2) annulation of trans-2-aroyl-3-styrylcyclopropane-1,1-dicarboxylates with nitriles is reported. The transformation involves the Lewis acid assisted formation of 1,5-dipolar intermediates from the cyclopropane dicarboxylates and nitriles followed by cyclization. The reactions proceed in a highly diastereoselective manner and afford 5-vinyl-1-pyrroline derivatives in 60-88% yields.