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Scavengers that capture reactive chemical substances are used to prevent the decomposition of materials. However, in the field of catalysis, the development of scavengers that inhibit background pathways has attracted little attention, although the concept will open up an otherwise inaccessible reaction space. In catalytic bromination, fast non-catalyzed background reactions disturb the catalytic control of the selectivity, even when using N-bromoamide reagents, which have a milder reactivity than bromine (Br 2 ). Here, we developed a trans-cyclooctene (TCO) bearing a 2-pyridylethyl group to efficiently retard background reactions by capturing Br 2 in bromocyclization using N-bromosuccinimide. The use of less than a stoichiometric amount of the TCO was sufficient to inhibit non-catalyzed reactions, and mechanistic studies using the TCO revealed that in situ-generated Br 2 provides non-catalyzed reaction pathways based on a chain mechanism. The TCO is useful as an additive for improving enantioselectivity and regioselectivity in catalytic reactions. Cooperative systems using the TCO with selective catalysts offer an alternative strategy for optimizing catalyst-controlled selectivity during bromination. Moreover, it also served as an indicator of Br 2 involved in catalytic reaction pathways; thus, the TCO was useful as a probe for mechanistic investigations into the involvement of Br 2 in bromination reactions of interest., (© 2023 Wiley-VCH GmbH.)

Catalysis by chiral weakly-coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non-nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O-tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins-type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Unlike carbonyl compounds, it has long been common understanding that excited imines show virtually no photoreactivity, and hence their properties and potential utility in chemical science remain largely unexplored. Now, a strategy is presented for eliciting latent photoreactivity of imines based on the introduction of a donor-acceptor (D-A) structure to extend the lifetime of their photoexcited states. A series of spectroscopic analyses and density functional theory calculations reveal unique photophysical properties of the D-A-type imines. Furthermore, the reactivity of the D-A-type imines is demonstrated by using them as a photoredox catalyst for atom-transfer radical addition. These findings illuminate a previously neglected chemical space in the field of photochemistry, which will be exploited by taking advantage of the inherent structural modularity of imines., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A site-divergent stereoselective Michael reaction system is developed based on the identification of two distinct catalysts. Cinchonidine-derived thiourea catalyzes the 1,4-addition of prochiral azlactone enolates to enynyl N-acyl pyrazoles in a highly diastereo- and enantioselective manner to give stereochemically defined alkynes, while P-spiro chiral triaminoiminophosphorane catalytically controls the stereoselective 1,6-addition and the consecutive γ-protonation of the vinylogous enolate intermediate to afford Z,E-configured conjugated dienes. This 1,6-adduct serves as a valuable precursor for the synthesis of a 2-amino-2-deoxy sugar., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A highly E-selective and enantioselective conjugate addition of 2-benzyloxythiazol-5(4H)-ones to β-substituted alkynyl N-acyl pyrazoles is achieved under the catalysis of a P-spiro chiral iminophosphorane. Simultaneous control of the newly generated central chirality and olefin geometry is possible with a wide array of the alkynyl Michael acceptors possessing different aromatic and aliphatic β-substituents, as well as the various α-amino acid-derived thiazolone nucleophiles. This protocol provides access to structurally diverse, optically active α-amino acids bearing a geometrically defined trisubstituted olefinic component at the α-position., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A highly stereoselective aza-Henry reaction of α-aryl nitromethanes with aromatic N-Boc imines was established by using C1 -symmetric chiral ammonium betaine as a bifunctional organic base catalyst. Various substituted aryl groups for both imines and nitromethanes were tolerated in the reaction, and a series of precursors for the synthesis of unsymmetrical anti-1,2-diaryl ethylenediamines was provided., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new, chiral bis-Ti(IV) oxide of type 3 has been designed and can be utilized for strong activation of aldehyde carbonyls, thereby allowing a new catalytic enantioselective allylation of aldehydes with allyltributyltin. The chiral bis-Ti(IV) catalyst (S,S)-3 can be readily prepared either by treatment of bis(triisopropoxy)titanium oxide with (S)-BINOL or by treatment of ((S)-binaphthoxy)isopropoxytitanium chloride with silver(I) oxide. Treatment of hydrocinnamaldehyde with allyltributyltin under the influence of chiral bis-Ti(IV) oxide (S,S)-3 generated in situ (10 mol %) in CH(2)Cl(2) afforded an allylation product in 84 % yield and with 99 % ee. This asymmetric allylation with non-racemic bis-Ti(IV) oxide 3 and partially resolved (S)-BINOL shows a positive nonlinear effect in correlation of the enantiopurity of the allylation product with the ee of the (S)-BINOL. Chiral bis-Ti(IV) oxide (S,S)-3 can also be utilized for related reactions such as asymmetric methallylation and propargylation of aldehydes with high enantioselectivity. This asymmetric approach provides a very useful way of obtaining high reactivity and selectivity through the simple introduction of the M-O-M unit into the design of chiral Lewis acid catalysts.