ChemInform Abstract: cis‐Selective Asymmetric Cyclopropanation of Olefins Catalyzed by Five‐Coordinate [RuCl(PNNP)]⁺ Complexes.

Abstract

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Preparation and Study of Reusable Polymerized Catalysts for Ester Hydrogenation

“…Ruthenium complexes with tetradentate PNNP ligands are active catalysts for a variety of enantioselective reactions, including hydrogenations and transfer hydrogenations of ketones, 75 epoxidations of olefins, 76 Diels−Alder reactions, 77 and cyclopropanations. 78 Saudan et al 15 reported that the Ru− 1) is active for ester hydrogenations (0.05 mol % 1, 5 mol % NaOMe, 100 °C, 49 atm H 2 , THF, 1 h, TON = 1980). Although 1 does not contain N−H groups, it is quite reasonable to expect that the imine groups are reduced to the corresponding amines during the initial stages of the hydrogenation.…”

Modular Enantioselective Synthesis of cis-Cyclopropanes through Self-Sensitized Stereoselective Photodecarboxylation with Benzothiazolines

“…The complexity of these catalysts 7,8 highlights the challenge to kinetically favor cis-cyclopropanes over their more stable trans diasteroisomers. Desirable catalytic approaches only offer limited scope 9 or low diastereo-and enantioselectivity. 10 In particular, the cis-cyclopropanation of alkenes employing benzylidenes is still problematic, due to the instability of the phenyldiazomethane precursors and the difficult taming of the resulting reactive intermediates.…”

“…To further explore the synthetic potential of this system, we obtained a cis-cyclopropane-modified phenylalanine amino acid (4u) in two steps from commercially available 4-iodophenylalanine. Moreover, the asymmetric total synthesis of the combretastatin A4 analogue 4v 6a was achieved in three steps starting from isovanillin (9) in 39% overall yield (Scheme 2B). To put these results in perspective, twice as many steps (including a resolution) were previously required to obtain this product in <10% overall yield from comparable materials.…”