A highly enantioselective stereodivergent synthesis of 3-aminooxindole derivatives was accomplished via asymmetric Mannich reaction between 2-substituted benzofuran-3-one and isatin-derived ketimines. Both anti and syn-selective chiral 3,3-disubstituted amino oxindoles bearing two adjacent tetrasubstituted stereogenic centers with high yield and excellent enantioselectivities were obtained using readily available cinchona-alkaloid derived organocatalysts. The control experiment revealed that oxygen atom present in the benzofuran ring played an important role in switching diastereodivergence. The obtained Mannich product was further transformed into a biologically important 2,3-dihydrobenzofuran derivative having three contiguous stereocenters with no loss of enantioselectivity.
The first highly diastereo- and enantioselective synthesis of armeniaspirol analogues was achieved using L-proline derived bifunctional squaramide which outperformed commonly used organocatalysts. Excellent yield (up to 99%) with diastereoselectivity (up to 99:1) and enantioselectivity (up to 99%) were obtained for a wide range of substrates.
The first thiourea catalysed asymmetric [3+2] cycloaddition reaction between azomethine imines and malanonitriles was developed. Using this novel synthetic strategy, hybrid molecules containing N,N-bicyclic pyrazolidinones fused with enaminonitriles were synthesized in good yields with excellent enantioselectivities (up to 98% ee).
A rhodium(III)-catalyzed, site-selective, CÀ H alkylation of quinoline N-oxides at C8 using bench-stable and commercially available diazo Meldrum's acid is reported. This straightforward protocol employs a widely available catalyst and enables the synthesis of a variety of 8-quinolinylacetic acid esters on gram scale without necessitating the preparation and use of an excess of air-sensitive organometallic reagents.
Enantiodivergent synthesis of 2,2′-disubstituted benzofuran-3-ones was accomplished with very good yield and stereoselectivity using squaramide organocatalysts.
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