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Quinone methides are fundamental intermediates for a wide range of reactions in which catalyst stereocontrol is often achieved by hydrogen bonding. Herein, we describe the feasibility of an intramolecular Friedel–Crafts 6π electrocyclization through ortho‐quinone methide iminiums stereocontrolled by a contact ion pair. A disulfonimide catalyst activates racemic trichloroacetimidate substrates and imparts stereocontrol in the cyclization step, providing a new avenue for selective ortho‐quinone methide iminium functionalization. A highly stereospecific oxidation readily transforms the enantioenriched acridanes into rotationally restricted acridiniums. Upon ion exchange, the method selectively affords atropisomeric acridinium tetrafluoroborate salts in high yields and an enantioenrichment of up to 93 : 7 e.r. We envision that ion‐pairing catalysis over ortho‐quinone methide iminiums enables the selective synthesis of a diversity of heterocycles and aniline derivatives with distinct stereogenic units. [ABSTRACT FROM AUTHOR]

A diastereo- and enantioselective formal [3+2] cycloaddition of N-tosylaziridines and aldehydes catalyzed by a Ni(ii)-bisoxazoline complex has been accomplished. The 1,3-oxazolidine products are obtained with high diastereoselectivity, good yields (up to 99%) and high ee values (up to 96% ee). The challenging long distant stereocenter control is achieved by a chirality transfer approach. [ABSTRACT FROM AUTHOR]

An efficient Y(OTf)3-catalyzed generation of azomethine ylides from donor-acceptor aziridines and their [3+2] cycloaddition with imines was developed. The method provides facile access to multisubstituted imidazolidines, which have been extensively used in organic synthesis. Furthermore, a three-component reaction on a gram scale and an asymmetric variation were also developed in this work. [ABSTRACT FROM AUTHOR]

A novel, mild, robust catalyst Y(OTf)3for C–C bond heterolysis of N-tosyl aziridines was developed and the resulting metallo-azomethine ylides may readily undergo [3+2] dipolar cycloaddition with an electron-rich olefin viaa stepwise reaction pathway with high regio- and diastereoselectivity leading to substituted pyrrolidines. [ABSTRACT FROM AUTHOR]

A novel catalytic exo/endoselectivity-controllable tandem heterocyclization/formal [4+3] cycloaddition was developed, which provides rapid, efficient and stereoselective access to highly fused polyheterocycles from readily available 2-(1-alkynyl)-2-alken-1-ones and 1,3-diphenylisobenzofuran under mild conditions. [ABSTRACT FROM AUTHOR]