Design of N-Spiro C2-Symmetric Chiral Quaternary Ammonium Bromides as Novel Chiral Phase-Transfer Catalysts: Synthesis and Application to Practical Asymmetric Synthesis of α-Amino Acids
02 Apr 2003-Journal of the American Chemical Society (American Chemical Society)-Vol. 125, Iss: 17, pp 5139-5151
TL;DR: The potential synthetic utility of the present method for the practical asymmetric synthesis of structurally diverse natural and unnatural alpha-amino acids has been demonstrated by its successful application to the facile asymmetric syntheses of (S)-N-acetylindoline-2-carboxylate, a key intermediate in the synthesis of the ACE inhibitor, and l-Dopa (l-3,4-dihydroxyphenylalanine) ester and its analogue.
Abstract: A series of C2-symmetric chiral quaternary ammonium bromides 10 and 11 have been designed as a new, purely synthetic chiral phase-transfer catalyst, and readily prepared from commercially available optically pure 1,1‘-bi-2-naphthol as a basic chiral unit. The details of the synthetic procedures of each requisite chiral binaphthyl subunit have been disclosed, and the structures of the assembled N-spiro chiral quaternary ammonium bromides 11a and 11f were unequivocally determined by single-crystal X-ray diffraction analysis. The reactivity and selectivity of these chiral ammonium bromides as chiral phase-transfer catalysts have been evaluated in the asymmetric alkylation of the benzophenone Schiff base of glycine ester 7 under mild liquid−liquid phase-transfer conditions, and the optimization of the reaction variables (solvent, base, and temperature) has also been conducted. Further, the scope and limitations of this asymmetric alkylation have been thoroughly investigated with a variety of alkyl halides, in...
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TL;DR: This review describes developments in the burgeoning field of asymmetric ion-pairing catalysis with an emphasis on the insights that have been gleaned into the structural and mechanistic features that contribute to high asymmetric induction.
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TL;DR: The palladium-catalyzed cross-coupling reaction between organoboron compounds and organic halides or triflates provides a powerful and general methodology for the formation of carbon-carbon bonds as discussed by the authors.
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