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DOI: 10.1055/s-0034-1379876
(R)-TRIP and (S)-TRIP – Very Recent Applications
Publication History
Publication Date:
23 January 2015 (online)


Introduction
(R)- and (S)-3,3′-bis(2,4,6-triisopropylphenyl)-1,1′-binaphthyl-2,2′-diylhydrogenphosphates, also known as (R)-TRIP and (S)-TRIP are chiral phosphoric acids (CPA’s) derived from BINOL. They are available from commercial sources, and they can be prepared through a three-step sequence that starts with a Kumada coupling between compound 1 and two equivalents of 2,4,6-(triisopropoxy)phenylmagnesiumchloride. This reaction is followed by a deprotection and a high-yielding phosphorylation step (Scheme [1a]).[1]
Since their first application in enantioselective organocatalytic hydrogenations by the List Group, in 2005,[2] these catalysts have been applied in numerous enantioselective transformations, including strategies involving cooperative catalysis.[3]



(A) Early in 2013, List and co-workers reported an asymmetric protonation of silyl ketene imines (SKI’s) catalyzed by (S)-TRIP or STRIP (a spiroderivative of TRIP).[4] During the catalyst screening both of these showed high efficiency. This transformation has no precedents in literature and showed to be a mild and straightforward strategy to access α-branched nitriles with high enantiopurity. |
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(B) Faber, Orthaber and co-workers reported an asymmetric allylation reaction between a zinc(II)-allylbutyrolactone species and (hetero)aromatic aldehydes using TRIP as catalyst.[5] DFT studies showed that a complex ion-pair involving TRIP, Zn2+ and substrates is formed prior to enantioenriched β-substituted α-methylenebutyrolactone formation. Although high enantioselectivities had been reached, a two-step total synthesis of natural product (S)-(–)-hydroxymatairesinol was also performed in order to demonstrate the applicability of the methodology. |
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(C) In order to expand the applicability of isochromenyliums in enantioselective transformations, an asymmetric [4+2] annulation between 2-hydroxystyrenes and isochromenyliums prepared in situ from 2-alkynylbenzaldehyes or 1-(2-alkynylphenyl)ketones was developed by Yao and co-workers.[6] Among the catalytic conditions investigated, the combination of Pd(OAc)2 with (S)-TRIP gave the best results. This cooperative catalytic system showed to be applicable for a broad spectrum of substrates. Good to excellent enantioselectivities were achieved. |
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(D) Still in 2013, an asymmetric synthesis of cyclic trifluoromethyldihydroquinazolines via a TRIP-catalyzed aza-Friedel–Crafts reaction between indoles and cyclic N-acylketimines was developed by Ma and co-workers.[7] This work was based on a previous report in which aryl-imines generated in situ from hemi-acetals were used as electrophiles.[8a] In 2011, Bolm and co-workers had also reported another example using trifluoropyruvate derived N-Boc-imines as electrophiles.[8b] |
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(E) Recently, the desymmetrization of pro-chiral diesters by an intramolecular transesterification catalyzed by TRIP was disclosed and had its scope explored by Petersen and co-workers.[9] The process showed to be scalable and robust, leading to the preparation of several enantioenriched lactones with all-carbon chiral quaternary centers, which showed to be useful small building blocks. |
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(F) Organocatalysed transfer hydrogenation of heteroaromatic compounds has been widely investigated over the last years. Recently, Zhou and co-workers reported the use of TRIP on the asymmetric hydrogenation of 2-aryl-quinolone-3-amines and 3-(trifluoromethyl)quinolones with up to 99% and 98% ee, respectively.[10a] [b] |
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(G) Taking advantage of a highly favoured heterodimerization of carboxylic acids with TRIP, List and co-workers investigated the desymmetrization of meso-aziridines and the kinetic resolution of terminal aziridines using this catalyst.[11] The catalytic system proved useful for the conversion of cyclic and acyclic aziridines into O-protected amino alcohols with high yields and enantioselectivities. This was the first report of a CPA’s catalyzed reaction using carboxylic acids as nucleophiles instead of only as additives, which has opened new perspectives in the field. |
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