Construction of 3,4-Dihydrocoumarin Derivatives with Adjacent Quaternary and Tertiary Stereocenters: Organocatalytic Asymmetric Michael Addition of 2-Oxochroman-3-carboxylate Esters totrans-β-Nitroolefins

Organocatalytic Asymmetric Addition of Aromatic α-Cyanoketones to o-Quinone Methides: Synthesis of 3,4-Dihydrocoumarins and Tetrasubstituted Chromans

The first organocatalytic asymmetric addition of aromatic α-cyanoketones to in situ-generated o-quinone methides has been developed. The products 3,4-dihydrocoumarin and tetrasubstituted chroman were obtained via addition of aromatic α-cyanoketones to in situ-generated o-quinone methides followed by treatment with 0.7 N HCl. With 10 mol % catalyst, the desired products were obtained in high enantio- and diastereoselectivities.

Highly enantioselective one-pot sequential synthesis of valerolactones and pyrazolones bearing all-carbon quaternary stereocentres

Highly enantiopure and bioactive δ-valerolactones and pyrazolones, bearing α-all-carbon quaternary stereocentres, were successfully and sequentially prepared via a one-pot procedure starting from readily available, inexpensive materials, catalysed by a new chiral squaramide under mild reaction conditions. An organocatalytic Michael reaction afforded the valerolactones, while a one-pot Michael-hydrazinolysis-imidization cascade yielded the pyrazolones. This procedure is economically efficient and environmentally benign.

Enantioselective Cyclopropanation/[1,5]-Hydrogen Shift to Access Rauhut-Currier Product

A Michael addition initiated cyclopropanation/[1,5]-hydrogen shift has been developed for the enantioselective synthesis of Rauhut-Currier products. The reaction of α-alkyl diazoesters and in situ generated o-quinone methides proceeds in the presence of chiral oxazaborolidinium ion, providing Z-stereocontrolled Rauhut-Currier products in high yields (up to 96%) with excellent Z/E selectivities (>20:1) and enantioselectivities (up to >99% ee). The synthetic utility was illustrated by conversion of the product to 3,4-dihydrocoumarins with two adjacent chiral stereocenters.

Reaction behaviour of arylamines with nitroalkenes in the presence of bismuth(iii) triflate: an easy access to 2,3-dialkylquinolines

We report the reaction behaviour of arylamines with nitroalkenes in the presence of bismuth(iii) triflate (10 mol%) and diacetoxyiodobenzene (10 mol%).

Recent Advances in Asymmetric Organocatalyzed Conjugate Additions to Nitroalkenes

The asymmetric conjugate addition of carbon and heteroatom nucleophiles to nitroalkenes is a very interesting tool for the construction of highly functionalized synthetic building blocks. Thanks to the rapid development of asymmetric organocatalysis, significant progress has been made during the last years in achieving efficiently this process, concerning chiral organocatalysts, substrates and reaction conditions. This review surveys the advances in asymmetric organocatalytic conjugate addition reactions to α,β-unsaturated nitroalkenes developed between 2013 and early 2017.

Role of Configuration at C6 in Catalytic Activity of l-Proline-Derived Bifunctional Organocatalysts

l-Proline-derived chiral bifunctional (thio)urea organocatalysts epi-PTU and epi-PU were newly synthesized, and their catalytic performances were compared with their C6 epimeric catalysts PTU and PU in various Michael reactions of nitrostyrene in terms of reactivities and stereoselectivities. The experimental results indicate that a proper relative stereochemistry at C2 and C6 in l-proline-derived bifunctional organocatalysts is important for successful catalysis and that catalysts (PTU and PU) with the 2S,6R configuration are much more efficient.