Cascade Cleavage of Three-Membered Rings in the Reaction of D-A Cyclopropanes with 4,5-Diazaspiro[2.4]hept-4-enes: A Route to Highly Functionalized Pyrazolines

Three-Component Synthesis of Substituted Perhydropyrans from β-Styrylmalonates, Aldehydes, and Alkoxyaluminum Dichlorides

A three-component synthesis of substituted dimethyl dihydro-2H-pyran-3,3(4H)-dicarboxylates in up to 80% yields by the reaction of β-styrylmalonates with aromatic or aliphatic aldehydes in the presence of ROAlCl2 prepared in advance either by exposure of EtAlCl2 with air access or by mixing equimolar amounts of AlCl3 with a primary or secondary alcohol has been developed. If EtAlCl2, itself, is used, dihydro-2H-pyran-3,3(4H)-diesters are not formed at all, while dimerization of styrylmalonates by (4 + 2)-annulation-type to give substituted tetrahydronaphthalenes is the main process. The possibility of using the CH-O-Al fragment of alkoxyaluminum dichlorides in cycloaddition reactions with α-CH-functionalization has been shown for the first time.

Lewis acid triggered N-alkylation of sulfoximines through nucleophilic ring-opening of donor-acceptor cyclopropanes: synthesis of γ-sulfoximino malonic diesters

Scandium triflate (Sc(OTf)₃) catalyzed, mild, and regioselective ring-opening reaction of donor-acceptor (D-A) cyclopropanes has been developed using sulfoximines for the synthesis of γ-sulfoximino malonic diesters. This protocol allows the synthesis of different N-alkyl sulfoximines in good to excellent yields (up to 94%) with broad functional group tolerance. In this process, N-H and C-C bonds are cleaved to form new C-N and C-H bonds. The feasibility of this method is supported by a gram-scale reaction and synthetic elaboration of the obtained product.

Synthesis of Spirocyclopropylpyrazole Derivatives via the Cascade Reaction of Alkylidenecyclopropanes with Pyrazolidinones and Trifluoroethanol

A novel synthesis of spirocyclopropylpyrazole derivatives tethered with a trifluoromethyl unit through an unprecedented cascade reaction of alkylidenecyclopropanes with pyrazolidinones and trifluoroethanol (TFE) has been developed. Mechanistically, the reaction involves...

Lewis Acid Mediated [3+2] and [3+3] Annulations of an Azomethine Imine with Donor–Acceptor Cyclopropanes

Two different Lewis acids were used for developing [3+2] and [3+3] regioselective cycloaddition reactions of an azomethine imine with activated cyclopropanes. Scandium(III) triflate catalyzes a [3+2] cycloaddition reaction of the azomethine imine with cyclopropanes to form tetrahydropyrazolone derivatives and tricyclic tetrahydrofuran derivatives in moderate yields. Complementary to this, a novel [3+3] cycloaddition reaction of the azomethine imine with activated cyclopropanes was developed by using EtAlCl2 as a Lewis acid to form hexahydropyridazinone derivatives in high regioselectivity.

Imidazol-5-one as an Acceptor in Donor-Acceptor Cyclopropanes: Cycloaddition with Aldehydes

Spiro[imidazol-5-one-4,1'-cyclopropanes] behave as donor-acceptor (D-A) cyclopropanes in a formal cycloaddition reaction with aldehydes. The activation of such type of cyclopropanes is achieved with an equivalent of Brønsted acid. The reaction proceeds in high yields of 51-92% and demonstrates moderate diastereoselectivity at the quaternary stereocenter, which is determined by the electron-donating nature of the aldehyde partner. The ease of separation of stereoisomers allowed the creation of a library of 44 spiroannulated tetrahydrofurans with various substitution patterns.

DBU-promoted ring-opening reactions of multi-substituted donor–acceptor cyclopropanes: access to functionalized chalcones with a quaternary carbon group

A strategy to synthesize highly stereoselective chalcones with alkylcyanoacetate subunits via DBU-promoted ring-opening reactions of multi-substituted D–A cyclopropanes has been developed without the requirement of a transition metal catalyst and extra solvent.

Convenient approach to polyoxygenated dibenzo[c,e]pyrrolo[1,2-a]azepines from donor–acceptor cyclopropanes

A convenient approach to polyoxygenated tetrahydrodibenzo[c,e]pyrrolo[1,2-a]azepines from the donor–acceptor cyclopropanes has been developed.