- Preparation of 2,5-anhydrohexitols (part I). Silicon-directed stereocontrolled cyclization
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Stereoselective chain-extension of carbohydrate aldehydes with the hydroxymethylating reagent (dimethylphenylsilyl)methylmagnesium chloride (1) followed by acid-mediated cyclization gives access to 2,5-anhydro-hexitols. The stereoselectivity of the ring closure depends on the nature of the acid, i.e., treatment with excess BF3·Et2O or catalytic H2SO4 leads to tetrahydrofurans with 2,3-cis or 2,3-trans configuration, respectively. Concomitant elimination is effectively suppressed in case of cyclisation of the more sterically hindered isopropyl substituted silanes.
- Van Delft, Floris L.,Valentijn, A. Rob P.M.,Van Der Marel, Gijs A.,Van Boom, Jacques H.
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p. 165 - 190
(2007/10/03)
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- Efficient Route to Highly Functionalized Tetrahydrofurans by Stereocontrolled Silicon-directed Cyclization
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Cyclization of 3,4,6-tri-O-benzyl-2,5-di-O-trimethylsilyl-1-deoxy-1-phenyldiisopropylsilyl-L-glucitol in the presence of BF3*Et2O or catalytic H2SO4 proceeds stereoselectively to give predominantly the fully benzylated 2,5-anhydro-L-glucitol derivative without occurrence of the Peterson elimination.
- Delft, F. L. van,Marel, G. A. van der,Boom, J. H. van
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p. 339 - 341
(2007/10/02)
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