Highly enantioselective Michael addition reactions of 2-substituted benzofuran-3(2H)-ones to nitroolefins

Direct Synthesis of 3-Coumaranones with Calcium Carbide as an Acetylene Source

A novel synthesis method for the construction of 3-coumaranones from the reaction of two molecules, calcium carbide and salicylaldehyde, was reported. Various 2-methyl-2-vinylbenzofuran-3(2H)-ones could be obtained in moderate yields in the absence of a metal catalyst. The salient features of this protocol involve widely available starting materials, an inexpensive and easy-to-handle alkyne source, and a cost-efficient route. The reaction mechanism was verified by density functional theory calculations of possible intermediates and corresponding transition states.

Catalytic enantioselective Michael addition of 2-substituted benzofuran-3-ones to 2-enoyl pyridines

An organocatalytic diastereo- and enantioselective synthesis of 2,2'-disubstituted benzofuran-3-ones bearing adjacent quaternary and tertiary stereocenters has been achieved through Michael addition of 2-substituted benzofuran-3-ones to 2-enoyl pyridines. Both the enantiomeric forms of the major diastereomer were obtained using l-proline derived squaramide and quinine derived bis squaramide with excellent yield (up to 98%) and stereoselectivities (up to 97 : 3 dr and 98% ee). The control experiment revealed that the presence and position of nitrogen atoms in the 2-enoylpyridine have played a crucial role in the stereochemical outcome of the product.

Stereodivergent Synthesis of 3-Aminooxindole Derivatives Containing Vicinal Tetrasubstituted Stereocenters via the Mannich Reaction

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.

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.

An enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones and 2-phthalimidoacrylates

A highly enantioselective conjugate addition reaction of 3-substituted benzothiophen-2-ones to 2-phthalimidoacrylates has been developed using a bifunctional tertiary-amine thiourea catalyst.

Organocatalytic and enantioselective Michael reaction between α-nitroesters and nitroalkenes. Syn/anti-selectivity control using catalysts with the same absolute backbone chirality

The asymmetric and catalytic Michael reaction between α-nitroesters and nitroalkenes has been studied in the presence of two bifunctional catalysts both containing the same absolute chirality at the carbon backbone. The reaction performed in similar conditions allows us to control the syn or anti selectivity of the Michael adduct obtaining good yields and high enantiocontrol in all cases.