In this article we describe a new asymmetric synthesis of highly substituted tetrahydrofurans through a Pd(PPh3)4-catalyzed formal [3 + 2]-cycloaddition of donor–acceptor cyclopropanes and ketenes. The desired structural motif was formed in moderate to excellent yields (42–84% for 16 examples), with excellent Z:E isomer diastereoselectivity (≥19:1 for 16 examples), and with good to excellent enantioselectivity in all cases examined (83–97% ee for 6 examples). The synthetic utility of the products was illustrated by a number of diastereoselective transformations into reduced tetrahydrofurans and spirocyclic tetrahydrofuran-barbiturate derivatives.
Last. Yury V. Tomilov(RAS: Russian Academy of Sciences)H-Index: 18
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A new ionic cyclopropanation process involving the addition of diazo esters to donor-acceptor cyclopropanes (DAC) activated by GaCl3 has been developed. The reactions occur via 1,2-zwitterionic gallium complexes with elimination of nitrogen in all cases to give 1,1,2,3-tetrasubstituted cyclopropanes as the main products. Also, a number of related processes with the formation of various polysubstituted cyclopropanes, alkenes, and cyclobutanes, including products of multiple diazo ester addition, ...
Last. Yury V. Tomilov(RAS: Russian Academy of Sciences)H-Index: 18
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Reactions of styrylmalonates with aromatic aldehydes in the presence of Lewis and Bronsted acids and their regularities have been studied in detail. Approaches to the synthesis of various polysubstituted 5,6-dihydropyran-2-ones, indenes, aryl-containing dienes and trienes, cyclopentadienes, and polycyclic lactones have been developed with chemo-, regio-, stereo-, and diastereoselectivity control. The mechanisms of these reactions were studied in depth using multinuclear NMR experiments, monitori...
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 a remarkable progress over the past several years. To date, different reactivity patterns of DACs’ has been successfully exploited in racemic/ stereoselective syntheses of various acyclic compounds or carbocycles with an impressive structural diversity. The thriving strategies has been successfully utilized in...
When InBr3-EtAlCl2 (15–30 mol%) was used as a dual Lewis acid system to promote the formal [3+2]-cycloaddition of enantioenriched donor–acceptor cyclopropanes with ketenes, cyclopentanones were formed in good to excellent yields (84–99%, 18 examples), and with excellent transfer of chirality (15 examples, 90% ee to >99% ee).