A redox neutral, highly enantioselective coupling between N-arylaminomethanes and N-sulfonyl aldimines was developed by harnessing the efficient catalysis of P-spiro chiral arylaminophosphonium barfate and a transition-metal photosensitizer under visible light irradiation. This mode of synergistic catalysis provides a powerful strategy for controlling the bond-forming processes of reactive radical intermediates.

A catalytic cycle initiated by the oxidative quenching of the excited photosensitizer (Ir*(ppy)3) is established for the enantioselective coupling between (N-arylamino)methanes and (N-methanesulfonyl)aldimines catalyzed by Ir-based photosensitizer and a chiral (arylamino)phosphonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate under visible light irradiation. This achievement clearly demonstrates the insensitivity of this redox-neutral asymmetric reaction to the sequence of the key redox events involved in the synergistic catalysis.

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.

Highly enantioselective protonation of α-halo and alkoxy carboxylic acid-derived ketene disilyl acetals is achieved by using P-spiro chiral diaminodioxaphosphonium barfate as a Brønsted acid catalyst, where the enantiofacial discrimination by the catalyst mainly stems from the recognition of the electronic difference between two substituents on the ketene disilyl acetal.

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 <i>O</i>,<i>N</i>,<i>N</i>,<i>O</i>-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.<br>

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 <i>O</i>,<i>N</i>,<i>N</i>,<i>O</i>-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.<br>

Enantioselective Protonation of -Hetero Carboxylic Acid-Derived Ketene Disilyl Acetals under Chiral Ionic Broensted Acid Catalysis. -(URAGUCHI, D.; KIZU, T.; OHIRA, Y.; OOI*, T.; Chem. Commun. (Cambridge) 50 (2014) 88, 13489-13491, http://dx.doi.org/10.1039/C4CC06081D ; Grad. Sch. Eng., Nagoya Univ., Chikusa-ku, Nagoya 464-8603, Japan; Eng.) -M. Tismer 13-048

Enantioselective aza-Michael addition to conjugated nitroenynes has been developed. P-Spiro heterochiral arylaminophosphonium barfate 1b·BArF effectively catalyzes the reaction, and the corresponding conjugate adducts, b-amino homopropargylic nitro compounds, are obtained in good chemical yields with high enantioselectivities.The catalytic asymmetric conjugate addition to extended Michael acceptors occupies a unique place in the realm of the stereoselective conjugate addition chemistry. 1,2 With rigorous control of both regio-and stereoselectivities, this Michael technology serves as an expedient means for the facile synthesis of functionalized chiral building blocks, which are not readily accessible by other asymmetric methodologies. As one of the suitable acceptors, nitroenynes possess their own attractive features because the conjugate addition to this class of substrate generally proceeds in a 1,4-manner and hence the corresponding adducts, homopropargylic nitro compounds, could enjoy the rich chemistry of functional-group transformations associated with the nitro 3 and alkynyl 4 moieties. [5][6][7] In 2006, the first example of this type of bond-forming reaction was reported by Trost et al. as a part of their study on the conjugate addition of a-hydroxy ketones to nitroolefins catalyzed by a chiral heterodinuclear metal complex. 5 More recently, Alexakis et al. developed highly enantioselective conjugate additions of carbonyl compounds and organometallic reagents to nitroenynes in the context of catalytic regio-and stereocontrols with extended nitroMichael acceptors. 6 However, these pioneering research efforts have focused on the use of carbon nucleophiles, and thus heteroatom-centered nucleophiles have never been employed in combination with nitroenynes despite the significant synthetic potential of the corresponding conjugate adducts, namely, chiral b-hetero-substituted homopropargylic nitro compounds. In this situation, we have been interested for some time in developing asymmetric conjugate addition of aniline derivatives to extended nitro-Michael acceptors using chiral ionic Brønsted acid 8,9 of type 1·BArF 10 as a catalyst on the basis of its effectiveness in aza-Michael reaction of simple conjugated nitroolefins. [11][12][13] Here, we present the results of this study by describing the highly enantioselective conjugate addition of 2,4-dimethoxyaniline to various nitroenynes efficiently catalyzed by P-spiro chiral arylaminophosphonium barfate 1b·BArF.We initiated our investigations by evaluating the ability of the chiral arylaminophosphonium barfates 1·BArF and 2·BArF as a Brønsted acid catalyst in the Michael donoracceptor combination of 2,4-dimethoxyaniline and nitroenyne 3a having a terminal phenyl substituent. The focus was then directed toward the relationship between the catalyst structure and the profile of reactivity and selectivity (Table 1). When 3a was treated with 2,4-dimethoxyaniline in toluene at 0°C under the influence of homochiral 2a·BArF with a phenyl group at 3,3¢-positions of one b...