Technology Spotlights

R(+) & S(-) Stericol Chiral Auxiliaries


Introduction
Introduction of chirality in organic molecules through the use of auxiliaries is a basic strategy in organic chemistry. Chiral benzylic alcohols are of particular interest because they often afford useful levels of stereoselection and are generally easy to cleave. The enantiomers of 1-(2,4,6-triisopropyl)phenylethanol ((R)- and (S)-Stericol®) are especially beneficial as chiral auxiliaries.
 
Representative Applications

[2+2] Cycloadditions
The use of these materials in this context was first reported by B. M. de Azevedo and Greene1 in a highly stereoselective [2+2] cycloaddition of dichloroketene to a chiral enol ether prepared from this alcohol. The dichlorocyclobutanones prepared in this manner (dr ≈ 19:1) are versatile synthetic intermediates that have been used to access a variety of natural products, including lactones1, cyclopentanones2, amino acids3, and alkaloids4 (Scheme 1).
 
Stericol Scheme 1

Similarly, the asymmetric [2+2] cycloaddition of dichloroketene was applied by Correia5 to chiral ene carbamate and by MacGee6 to α,β-unsaturated esters. In both cases, the Stericol® controlled reactions provided the same diastereomeric ratio (4:1), which was the highest obtained for these ene carbamate derivatives (Scheme 2).
Stericol Scheme 2

References:
  1. de Azevedo, M. B. M.; Greene, A. E. J. Org. Chem. 1995, 60, 4940-4942.
  2. Kanazawa, A.; Delair, P.; Pourashraf, M.; Greene, A. E. J. Chem. Soc. Perkin Trans. 1997, 1911-1912.
  3. Nebois, P.; Greene, A. E. J. Org. Chem. 1996, 61, 5210-5211; Ceccon, J.; Poisson, J. F.; Greene, A. E. Synlett 2005, 1413-1416.
  4. Kanazawa, A.; Gillet, S.; Delair, P.; Greene, A. E. J. Org. Chem. 1998, 63, 4660-4663; Delair, P.; Brot, E.; Kanazawa, A.; Greene, A. E. J. Org. Chem. 1999, 64, 1383-1386; Pourashraf, M.; Delair, P.; Rasmussen, M. O.; Greene, A. E. J. Org. Chem. 2000, 65, 6966-6972; Rasmussen, M. O.; Delair, P.; Greene, A. E. J. Org. Chem. 2001, 66, 5438-5443; Roche, C.; Delair, P.; Greene, A. E. Org. Lett. 2003, 5, 1741-1744; Muniz, M. N.; Kanazawa, A.; Greene, A. E. Synlett 2005, 1328-1330; Roche, C.; Kadlecikova, K.; Veyron, A.; Delair, P.; Philouze, C.; Greene, A. E.; Flot, D.; Burghammer, M. J. Org. Chem. 2005, 70, 8352-8363; Ceccon, J.; Greene, A. E.; Poisson, J. F. Org. Lett. 2006, 4739-4742.
  5. Miranda, P. C. M. L.; Correia, C. R. D. Tetrahedron Lett. 1999, 40, 7735-7738.
  6. MacGee, D. I.; Mallais, T. C.; Mayo, P. D. M.; Strunz, G. M. Tetrahedron. 2006, 62, 4153-4161.

Novel C–C bond forming reactions: Preparation of β,γ-unsaturated silyl sulfinates
The high level of stereoinduction achieved with Stericol® was further demonstrated by Vogel and coworkers1 in a new carbon-carbon bond forming reaction. In this process, a 1-alkoxy-1,3-diene reacted with sulfur dioxide in the presence of a Lewis acid to generate a zwitterionic intermediate, which was trapped by a trimethylsilyl enol ether to give a β,γ-unsaturated silyl sulfinate (Scheme 3). The Stericol® derived alkoxydiene gave the highest diastereomeric ratios (up to 25:1).
Stericol Scheme 3
References:
  1. Narkevitch, V.; Schenk, K.; Vogel, P. Angew. Chem., Int. Ed. 2000, 39, 1806-1808; Bouchez, L. C.; Turks, M.; Dubbaka, S. R.; Fonquerne, F.; Craita, C.; Laclef, S.; Vogel, P. Tetrahedron 2005, 61, 11473-11487; Narkevitch, V.; Megevand, S.; Schenk, K.; Vogel, P. J. Org. Chem. 2001, 66, 5080-5093.


Asymmetric oxidation of benzenesulfenates
In order to prepare stereodefined phophorus-sulfur chelating ligands, Drabowicz and coworkers1 studied the asymmetric oxidation of chiral benzenesulfenates to the corresponding sulfinates (Scheme 4). Among the chiral alcohols tested, the Stericol® derived benzensulfenate gave the highest diastereomeric ratio (13:1).
Stericol Scheme 4
References:
  1. Hamel, M.; Grach, G.; Abrunhosa, I.; Gulea, M.; Masson, S.; Vazeux, M.; Drabowicz, J.; Mikolajczyk, M. Tetrahedron: Asymmetry 2005, 16, 3406-3415.
Stericol® also has potential applications as an agent for resolution, deracemization, and determination of stereopurity.


Product Information
Product # Product Name Structure Add to Cart
672599 (R)-(+)-1-(2,4,6-Triisopropylphenyl)ethanol (R)-(+)-1-(2,4,6-Triisopropylphenyl)ethanol
672483 (S)-(–)-1-(2,4,6-Triisopropylphenyl)ethanol (S)-(–)-1-(2,4,6-Triisopropylphenyl)ethanol
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