2,8′-Disubstituted-1,1′-Binaphthyls: A New Pattern in Chiral Ligands

The 2,8′-isomer of NOBIN (1) has been synthesized in both enantiomeric forms by using Suzuki coupling as the key step to construct the 1,1′-axis, followed by Hartwig–Buchwald amination. This new series is configurationally as stable as the conventional 2,2′-disubstituted 1,1′-binapthyls. Acetamide (R)-(−)-2 has been found to catalyze Michael addition of a glycine-derived Ni complex to methyl acrylate, giving L-glutamic acid of 92 % ee under mild, phase-transfer conditions (NaH, RT, 2 min). The title binaphthyls 19 and 26, which are the positional isomers of 2-methoxy-2′-(diphenylphosphino)-1,1′-binaphthyl (MOP, 19) and 2-amino-2′-hydroxy-1,1′-binaphthyl (NOBIN, 26), have been synthesized by Suzuki coupling as the key step (10 + 15→18), followed by functional group transformations, involving CP and CN bond formation (18→19 and 18→23). Racemic intermediate 22 was resolved by co-crystallization with N-benzylcinchonidinium chloride and the absolute configuration determined by X-ray crystallography. These novel binaphthyls are configurationally stable and, as such, potentially usable as chiral ligands in asymmetric reactions. Michael addition of the glycine-derived enolate 40 to methyl acrylate, carried out in the presence of (R)-(−)-27 as the chiral phase-transfer catalyst, afforded L-glutamic acid (S)-(+)-43 of 92 % ee (after hydrolysis of the primary product). 2,8′-Disubstituované-1,1′-binaftyly, zejména polohové isomery MOPu (19) a NOBINu (26), byly syntetizovány s použitím Suzukiho reakce jako klíčového kroku (10 + 15→18), po němž následovala transformace funkčních skupin, zahrnující tvorbu C-P a C-N vazeb (18→19 a 18→23). Racemický meziprodukt 22 byl rozštěpen na enantiomery krystalizací s N-benzylcinchonidinium chloridem a jeho absolutní konfigurace byla stanovena pomocí rentgenostrukturní krystalografie. Tyto nové binaftyly jsou konfiguračně stabilní a tudíž potenciálně využitelné jako chirální ligandy v asymetrických reakcích. Michaelova adice enolátu 40, odvozeného z glycinu, na methyl metakrylát, prováděná v přítomnosti (R)-(−)-27 jako chirálního katalyzátoru fázového přenosu, poskytla L-glutamovou kyselinu (S)-(+)-43 s 92 % ee (po hydrolýze primárního produktu). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2002/f3814_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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