1,2-Cyclopropanated glucose derivatives

Stereoselective cyclopropanation of acyclic allylic alcohols glucose-derived chiral auxiliary24 1... 

On the other hand, with 1,2-disubstituted or certain trisubsti-tuted olefins, the chiral ligand also influences the trans/cis selectivity. For example, treatment of a glucose-derived enol ether with diazomethyl acetate in the presence of Cu[(5, 5)-/-Bu-box] (OTf) complex affords the cyclopropanation product with an excel-... 

Two examples of the applicability of anomeric carbenes were reported by VaseUa et al. [167,168]. The first demonstrated the utility of olefinic substrates such as Al-phenylmaleimide, acrylonitrile and dimethylmaleate for the formation of glycosidic cyclopropanes. The carbene precursor in this example was the glucose-derived diazirine. As shown in Scheme 7.55, the use of dimethylmaleate produced a mixture of diastereomers with a combined yield of 72%. Although not presented as a schematic, the second and more dramatic example was used to functionalize fullerenes. 

Scheme 6.28. Asymmetric cyclopropanation of allylic alcohols (a) Using a glucose-derived auxiliary [106] (b) A cyclohexane diol auxiliary [107].

Asymmetric cyclopropanation. Cyclopropanation of substituted ally lie alcohols (1) attached to a carbohydrate derived from D-glucose with (C2Hs)2Zn and CH2I2 (excess) can proceed with high diastereoselectivity. The triflate of the product (2) when heated in... 

The natural products (+)-calystegine and its enantiomer have been synthesized from D-glucose via the Ferrier rearrangement product 198. Ring expansion of the cyclopropane derivative 199 gives 200, converted to either 201 or 202, precursors to the natural product 203 or its enantiomer 204 respectively (Scheme 48). [preliminary report see Vol. 26, p. 314-5, ref. 73]. 

The diastereoselective hydroxyl-directed cyclopropanation shown in Scheme 22 was one of a number studied which proceed with high stereoselectivity. The chiral auxiliary could be removed as indicated, and use of the equivalent derivative of 6-deoxy-L-glucose gave the enantiomeric cyclopropylmethanols.l 13... 

As an example of the use of this methodology in total synthesis, the zirconocene-promoted ring contraction was the key step in the route to (+)-epiafricanol (100) reported by Paquette et al. [78]. Vinyl pyranose 95, obtained from D-glucose in 12 steps, was treated with Cp2Zr in toluene at -78°C and then with boron trifluoride etherate at room temperature, affording vinyl cyclopentane 96 in a 63% yield. Conversion of 96 to ketone 97 with periodinane as the oxidant in the presence of sodium bicarbonate and addition of the lithium derivative to 4,4-dimethyl-5-iodo-l-pentene 98 gave rise to 99. Cyclization of 99 by RCM followed by cyclopropanation finally afforded the desired product 100 (Scheme 3.39). 

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