Asymmetric Construction of 2,3-Dihydroisoxazoles via an Organocatalytic Formal [3 + 2] Cycloaddition of Enynes with N-Hydroxylamines.

An organocatalytic asymmetric formal [3 + 2] cycloaddition of enynones with N-hydroxylamines has been described. A newly designed multifunctional organocatalyst was found to be highly effective, and the method allowed the synthesis of a variety of 2,3-dihydroisoxazoles in good yields with excellent enantioselectivity.

Organocatalytic enantioselective synthesis of 2,3-allenoates by intermolecular addition of nitroalkanes to activated enynes.

The first efficient intermolecular addition of nitroalkanes to activated enynes for asymmetric synthesis of 2,3-allenoates is described. It is a new addition to the limited available strategies for catalytic asymmetric synthesis of allenoates. Enabled by a new bifunctional catalyst, a range of trisubstituted allenoates can be obtained in excellent chemical and optical purity. These allenoate products with a pendant 2-nitroethyl α-substituent are useful chiral building blocks.

A base-promoted tandem cycloaddition/air oxidation reaction of electron-deficient conjugated enynes and hydrazines: synthesis of highly substituted pyrazoles.

Rapid access: A base-mediated cycloaddition/oxidation reaction of hydrazines and electron-deficient 1,3-conjugated enynes gives pyrazole derivatives, some of which are not easily accessible by other methods (see scheme). The reaction conditions are mild, thus enabling a variety of functional groups to be tolerated.

DBU-catalyzed tandem additions of electron-deficient 1,3-conjugated enynes with 2-aminomalonates: a facile access to highly substituted 2-pyrrolines.

An efficient, metal free approach to highly substituted 2-pyrrolines by DBU-catalyzed tandem additions (a formal [3+2] cycloaddition) of electron-deficient 1,3-conjugated enynes and 2-aminomalonates under mild conditions was developed.

Organocatalytic hetero [4+2] cycloaddition reactions of 2-(1-alkynyl)-2-alkene-1-ones: metal-free access to highly substituted 4H-pyrans.

Highly substituted 4H-pyrans can be smoothly synthesized from readily available 2-(1-alkynyl)-2-alkene-1-ones by DBU- or n-Bu(3)P catalyzed hetero-[4+2] cycloaddition reactions, in which 2-(1-alkynyl)-2-alkene-1-ones act as both heterodiene and heterodinenophile.

Highly substituted 2,3-dihydroisoxazoles by Et(3)N-catalyzed tandem reaction of electron-deficient 1,3-conjugated enynes with hydroxylamines.

An Et(3)N-catalyzed tandem reaction of electron-deficient 1,3-conjugated enynes with hydroxylamines was developed which provided rapid, metal-free, and regioselective access to highly substituted multifunctionalized 2,3-dihydroisoxazoles under mild conditions. The reactions of 3-(2-arylethynyl)-4H-chromen-4-ones with hydroxylamines afford beta-amino enones under the same reaction conditions.