Stereoselective electrocatalytic transformation of malonate and alkylidenecyanoacetates into (E)-3-substituted 2-cyanocyclopropane-1,1,2-tricarboxylates

Electrolysis of malonate and alkylidenecyanoacetates in alcohols in an undivided cell in the presence of NaBr results in stereoselective formation of (E)-3-substituted 2-cyanocyclopropane-1,1,2-tricarboxylates in 75-90% yields.     

Electrocatalytic transformation of dialkyl malonates and arylidene- or alkylidenemalononitriles into dialkyl esters of 3-substituted 2,2-dicyanocyclopropane-1,1-dicarboxylic acids

Electrolysis of alcoholic solutions of dialkyl malonates and arylidene- or alkylidenemalononitriles in the presence of NaBr in an undivided cell gave dialkyl esters of 3-substituted 2,2-dicyanocyclopropane-1,1-dicarboxylic acids in 60–90% yields. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1547–1552, July, 2005.     

Stereospecific Reactions of Donor–Acceptor Cyclopropanes with Thioketones: Access to Highly Substituted Tetrahydrothiophenes

Lewis‐acid‐catalyzed reactions of 2‐substituted cyclopropane 1,1‐dicarboxylates with thioketones are described. Highly substituted tetrahydrothiophenes with two adjacent quaternary carbon atoms were obtained in a stereospecific manner under mild conditions and in high yield when using AlCl₃ as Lewis acid. Moreover, an intramolecular approach was successfully implemented to gain access to sulfur‐bridged [n .2.1] bicyclic ring systems. Conversion of selenoketones, the heavier analogues, under similar conditions resulted in the formation of various tetrahydroselenophenes.     

Asymmetric Copper-Catalyzed Carbomagnesiation of Cyclopropenes

The highly diastereo- and enantioselective formation of polysubstituted cyclopropanes was easily achieved through the asymmetric copper-catalyzed carbomagnesiation reaction of nonfunctionalized cyclopropene derivatives. The carbometalated species generated in situ readily undergo C−C and C−X bond-forming reactions with various electrophiles with complete retention of configuration.     

Reactions of Donor–Acceptor Cyclopropanes with Naphthoquinones: Redox and Lewis Acid Catalysis Working in Concert

Reactions of 2‐arylcyclopropane dicarboxylates with naphthoquinones are reported. The key feature was the use of catalytic amounts of SnCl₂, which acts as both an electron donor and a Lewis acid. By an in situ umpolung of naphthoquinone the formerly electrophilic species is converted into a nucleophile that is able to trigger the ring‐opening of the three‐membered ring with formation of a new C−C bond. Treatment of these products with base under oxidative conditions resulted—through loss of methyl formate—in cyclopentannulated products with fully conjugated π systems exhibiting intensive absorptions in the visible range.     

Regioselective Synthesis of Pyrazoles and Isoxazoles with Cyclopropanated Side‐Chain

Pyrazoles and isoxazoles with cyclopropanated side‐chain were prepared by cyclization of cyclopropanated 1,3,5‐tricarbonyl compounds with hydrazine and hydroxylamine, respectively. The regioselectivity is influenced by the reaction conditions.     

Uncovering the Neglected Similarities of Arynes and Donor–Acceptor Cyclopropanes

Arynes and donor–acceptor (D–A) cyclopropanes are two classes of strained systems having the potential for numerous applications in organic synthesis. The last two decades have witnessed a renaissance of interest in the chemistry of these species primarily because of the mild and robust methods for their generation or activation. Commonly, arynes as easily polarizable systems result in 1,2‐disubstitution, whereas D‐A cyclopropanes as polarized systems lead to 1,3‐bisfunctionalization thereby showing striking similarities. Transformations with 1,2‐ and 1,3‐dipoles afford cyclic structures. With arynes, emerging four‐membered rings as intermediates might react further, whereas the analogous five‐membered rings obtained from D–A cyclopropanes are most often the final products. However, there are a few cases where these intermediates behave surprisingly differently. This Minireview highlights the parallels in reactivity between arynes and D–A cyclopropanes thereby shedding light on the neglected similarities of these two reactive species.