Carbohydrate template

From a structural point of view, the carbohydrate template can have either furan or pyran rings although in some cases open chain structures can be formed. A large variety of aldopentoses (e.g. d- and L-arabinose, D-ribose, D-xylose), aldohexoses (e.g. D-glucose, D-mannose, D-galactose) as well as ketohexoses (e.g. D-fructose, L-sorbose) can be used as scaffolds. 

When comparing these results with those previously obtained using carbohydrate-based vinyl ethers as chiral dienophiles, this improved facial diastereoselectivity to heterodienes under similar conditions is noteworthy.81 The efficient chiral transfer in the second example might mostly be attributed to the specific architecture of the l,2 5,6-di-0-isopropylidene-a-D-glucofuranose moiety.Those findings open the way to develop well-defined spiro-carbohydrate templates towards improved auxiliaries for chirality transfer in a wide range of syntheses. 

Finally, this free radical approach is a good way to form carbocycles on the carbohydrate templates, provided the tether between the radical center and the olefin is a carbon chain [93,99-101], see also other contributions of this book describing the carbohydrate to carbocycle transformations. 

J. Marco-Contelles, The Paulson-Khand reaction on carbohydrate templates I. Synthesis of bis-heteroannulated-phyranosides, Tetrahedron Lett. 55 5059 (1994). 

G. J. Engelbrecht and C. W. Holzapfel, Stereoselective palladium catalyzed cyclization on carbohydrate templates—a route to chiral cyclopentanes and some heterocyclic analogs, Tetrahedron Lett. 32 2161 (1991). 

I.-F. Nguefack, V. Bolitt, and D. Sinou, Palladium-mediated cyclization on carbohydrate templates. 2. Synthesis of enantiopure tricyclic compounds, J. Org. Chem., 62 (1997) 6827-6832. 

M. K. Gurjar, S. K. Das, and U. K. Saha, Zaragozic acid A interesting observations in anhydro-ring formation of densely functionalised carbohydrate templates, Tetrahedron Lett., 35 (1994) 2241-2244. 

This methodology was successfully used for the synthesis of a-disposed sulfamidates of diverse carbohydrate templates (D-glucose, D-galactose, L-rhamnose) <2004JA6234, 2004CEJ5581>. 

The higher steric demand of carbohydrate templates containing the pivaloyl ester usually results in a higher stereoselectivity in their reactions compared to those of the acetyl-protected analogues [13]. 

During this reaction, two new chiral centres are formed. The formation of one diasteromer with high selectivity shows the potential of the chirality transfer from carbohydrate templates. Conversion of the 2,3-diphenyl alanine into the corresponding 3-amino propanol proved the erythro configuration of the major diaster-eomer. 

Carbohydrate templates have provided interesting applications of the Patemo-BUchi reaction. In a series of papers, Araki has demonstrated the feasibility of oxetane formation from glucals. - Photocy-... 

Kunz, H, Mueller, B, Schanzenbach, D, Diastereoselective Diels-Alder reactions using carbohydrate templates, Angew. Chem. Int. Ed., 26, 267- 269, 1987. 

Pfrengle, W, Kunz, H, Hetero Diels-Alder reactions on a carbohydrate template stereoselective... 

Kunz, H, Pfrengle, W, Asymmetric synthesis on carbohydrate templates stereoselective Ugi synthesis of a-amino acid derivatives, J. Am. Chem. Soc., 110, 651-652, 1988. 

Other methods that rely on the use of the carbohydrate template to construct fused carbocycles have been successfully investigated as strategies for the formation of carbocycles from sugars. Chirality transfer from the sugar to the new carbocycle is observed for these reactions. These annulation reactions are the subject of the second part of this section. 

Gurjar, M K, Das, S K, Sadalapure, K S, Zaragozic acid unusual stereochemical dependence in anhydride formation of carbohydrate templates. Tetrahedron Lett., 36, 1933-1936, 1995. 

Molino, B F, Magdzinski, L, Fraser-Reid, B, Pyranosidic homologation Part I extending the carbohydrate template via C-6 and C-4 + Part II, Tetrahedron Lett., 24, 5819-5822, 1983. 

Pfrengle, W, Kunz, H, Hetero Diels-Alder reactions on a carbohydrate template stereoselective synthesis of (S)-anabasine, J. Org. Chem., 54, 4261-4263, 1989. 

A similar attempt to employ a carbohydrate template for asymmetric induction in the [1,2] Wittig rearrangement of methyl 6-0-benzyl-2.3,4-tri-O-methyl-a-D-glucopyranoside was modestly successful, affording a 2 1 mixture of diastereomeric products51. 

Asymmetric induction using a transition metal complex (67), use of a carbohydrate template (68), and use of the chiral lactone 49 (69) or ester 50 (70) have all given effective syntheses of stereospecifically labeled samples of glycine. A further synthesis by Santaniello etal. (71, 72) has used glutamate decarboxylase to prepare labeled samples of y-aminobutyric acid 51 (Scheme 16). On cyclization, protection, and oxidation, these gave the labeled enamides 55, which were degraded to the labeled samples of glycine 23 (71, 72). 

Herriott used the phosphorus epimers of 0-(-)-menthyl methylphenylphosphinoth-ioate to demonstrate the almost quantitative stereospecificity in the reaction with mCPBA by contrast, the use of trifluoroperoxyacetic acid was less successful, with a retention to inversion ratio of 21 79. A further feature in favour of mCPBA is the independence of its activity relative to solvent. Other extensive correlations were made by Inch and coworkers during investigations into the stereochemistry of displacement reactions at phosphorus in compounds based on a carbohydrate template 81 by means of structural assignments based on infrared absorption frequencies for the P=0 bond together with P NMR chemical shifts, they showed that mCPBA oxidation of thiophosphoryl or selenophosphoryl bonds (A or B = =S or =Se, B or A = Me or Ph) occurred highly stereoselectively with the formation of the phosphonate ester with retained stereochemistry ... 

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