Catalytic enantioselective allyl- and crotylboration of aldehydes using chiral diol x SnCl4 complexes. optimization, substrate scope and mechanistic investigations.
J Am Chem Soc. 2008 Jul 02; 130(26):8481-90.JA

Abstract

We report a novel class of C2-symmetric chiral diols derived from the hydrobenzoin skeleton. The combination of these diols with SnCl4 under Yamamoto's concept of Lewis acid assisted Brønsted acidity (LBA catalysis) leads to high levels of asymmetric induction in the allylboration of aldehydes by commercially available allylboronic acid pinacol ester 1a. The corresponding homoallylic alcohol products of synthetically useful aliphatic aldehydes are obtained in excellent yields with up to 98:2 er. This combined acid manifold is also efficient in catalyzing the diastereo- and enantioselective crotylboration of aldehydes, thus providing the propionate units in >95:5 dr and up to 98:2 er. The X-ray crystal structure of the optimal diol x SnCl4 complex, Vivol (4m) x SnCl4, unambiguously shows the Brønsted acidic character of this LBA catalyst and its highly dissymmetrical environment. Further controls have ruled out a possible boron trans-esterification mechanism with the chiral diol and point to LBA catalyst-derived activation of the pinacol allylic boronates 1. Due to slow dissociation of the diol x SnCl4 complex, a small excess of diol is required in order to suppress a competing racemic cycle catalyzed by free SnCl4.

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Publisher Full Text (DOI)

Authors+Show Affiliations

Rauniyar V

Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.

Zhai H

No affiliation info available

Hall DG

No affiliation info available

MeSH

AldehydesBoranesCatalysisStereoisomerismTin Compounds

Pub Type(s)

Journal Article

Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

18540580

Citation

Rauniyar, Vivek, et al. "Catalytic Enantioselective Allyl- and Crotylboration of Aldehydes Using Chiral Diol X SnCl4 Complexes. Optimization, Substrate Scope and Mechanistic Investigations." Journal of the American Chemical Society, vol. 130, no. 26, 2008, pp. 8481-90.

Rauniyar V, Zhai H, Hall DG. Catalytic enantioselective allyl- and crotylboration of aldehydes using chiral diol x SnCl4 complexes. optimization, substrate scope and mechanistic investigations. J Am Chem Soc. 2008;130(26):8481-90.

Rauniyar, V., Zhai, H., & Hall, D. G. (2008). Catalytic enantioselective allyl- and crotylboration of aldehydes using chiral diol x SnCl4 complexes. optimization, substrate scope and mechanistic investigations. Journal of the American Chemical Society, 130(26), 8481-90. https://doi.org/10.1021/ja8016076

Rauniyar V, Zhai H, Hall DG. Catalytic Enantioselective Allyl- and Crotylboration of Aldehydes Using Chiral Diol X SnCl4 Complexes. Optimization, Substrate Scope and Mechanistic Investigations. J Am Chem Soc. 2008 Jul 2;130(26):8481-90. PubMed PMID: 18540580.

* Article titles in AMA citation format should be in sentence-case

TY - JOUR T1 - Catalytic enantioselective allyl- and crotylboration of aldehydes using chiral diol x SnCl4 complexes. optimization, substrate scope and mechanistic investigations. AU - Rauniyar,Vivek, AU - Zhai,Huimin, AU - Hall,Dennis G, Y1 - 2008/06/07/ PY - 2008/6/11/pubmed PY - 2008/8/1/medline PY - 2008/6/11/entrez SP - 8481 EP - 90 JF - Journal of the American Chemical Society JO - J Am Chem Soc VL - 130 IS - 26 N2 - We report a novel class of C2-symmetric chiral diols derived from the hydrobenzoin skeleton. The combination of these diols with SnCl4 under Yamamoto's concept of Lewis acid assisted Brønsted acidity (LBA catalysis) leads to high levels of asymmetric induction in the allylboration of aldehydes by commercially available allylboronic acid pinacol ester 1a. The corresponding homoallylic alcohol products of synthetically useful aliphatic aldehydes are obtained in excellent yields with up to 98:2 er. This combined acid manifold is also efficient in catalyzing the diastereo- and enantioselective crotylboration of aldehydes, thus providing the propionate units in >95:5 dr and up to 98:2 er. The X-ray crystal structure of the optimal diol x SnCl4 complex, Vivol (4m) x SnCl4, unambiguously shows the Brønsted acidic character of this LBA catalyst and its highly dissymmetrical environment. Further controls have ruled out a possible boron trans-esterification mechanism with the chiral diol and point to LBA catalyst-derived activation of the pinacol allylic boronates 1. Due to slow dissociation of the diol x SnCl4 complex, a small excess of diol is required in order to suppress a competing racemic cycle catalyzed by free SnCl4. SN - 1520-5126 UR - https://www.unboundmedicine.com/medline/citation/18540580/Catalytic_enantioselective_allyl__and_crotylboration_of_aldehydes_using_chiral_diol_x_SnCl4_complexes__optimization_substrate_scope_and_mechanistic_investigations_ L2 - https://doi.org/10.1021/ja8016076 DB - PRIME DP - Unbound Medicine ER -

Tags

Catalytic enantioselective allyl- and crotylboration of aldehydes using chiral diol x SnCl4 complexes. optimization, substrate scope and mechanistic investigations.J Am Chem Soc. 2008 Jul 02; 130(26):8481-90.JA