Asymmetric cyclopropanation with diazoacetates induced by carbohydrate-derived chiral auxiliaries

Alkenyl β-d-galactopyranoside derivatives as efficient chiral templates in stereoselective cyclopropanation and epoxidation reactions

“…This cyclopropanation reaction had been studied in allyl b-D-glucopyranosides in toluene, which takes place with high diastereoisomeric excesses. 8b, [9][10][11][12] As our products, with a free OH at at the 2-and 3-position of the sugar, are not very soluble in toluene, we decided to use CH 2 Cl 2 as the solvent, and chose for this assay, compounds 3 and 6 (Scheme 4). Compounds 23 and 24 were obtained in 57% and 22% of diastereoisomeric excess, respectively (determined by 1 …”

“…7 There are only a few precedents for the stereoselective synthesis of cyclopropanes using carbohydrates as chiral auxiliaries. [8][9][10][11][12] Our group has recently published the stereoselective cyclopropanation (using the diiodomethane/diethyl zinc system) of a wide range of alkenes linked via an acetal function to different backbones of sugar moieties. 13,14 It is important to note that the union of the olefin to the carbohydrate via an acetal function allowed the easy separation of the new chiral cyclopropane fragment and the chiral auxiliary by mild acid hydrolysis.…”

“…In the present case, the substrates chosen as carriers of the double bond for the stereoselective transformations are a wide range of allyl alcohols that join to the chiral auxiliary via a glycosidic bond with D-galactose as the carbohydrate inducer of chirality. We chose this carbohydrate as the auxiliary; (a) because there are few references describing the use of chiral auxiliaries derived from D-galactose in these reactions on double bonds, 24 and thus to assess its capacity as a chirality agent; and (b) because Dgalactose is a frequent sugar in glycolipid complexes such as glycerolipids, phosphatidic acids and sphingolipids, substances that have gained great interest as regulatory agents of cell proliferation, and thus are possibly useful in the treatment of cancer. 25 The synthesis of the derivatives or analogues of these natural products is a focus of attention.…”

Functionalization of the Anomeric C–H Bond of Carbohydrates: Old Strategies and New Opportunities

“…Diazo sugars were used early on to map interactions between oligosaccharides and proteins by making covalent bonds with amino acid residues under photolytic conditions (Figure 2, part a). 32 Later, such sugars were employed as chiral auxiliaries for stereoselective intermolecular cyclopropanations 33 or insertions into silicon-hydrogen bonds (Figure 2, part b). 34 In addition, the formation of sulfonium ylides from diazo sugars has been used to modify peptides 35 and to prepare the central core of a phytotoxin.…”

The use of 1,2-O-isopropylidene-α-d-xylofuranose as a chiral auxiliary in asymmetric cyclopropanation reactions

“…13,21,22 Carbohydrates contain several functional groups and stereogenic centres in one molecular unit, which allows the use of carbohydrates as tools in stereochemical differentiations, as the starting materials in syntheses of interesting enantiopure compounds, [23][24][25][26] as chiral templates in asymmetric transformations 27 and as chiral auxiliaries in stereoselective syntheses. [28][29][30][31][32][33][34][35][36][37] However, there are few precedents for the use of carbohydrates as chiral auxiliaries in the asymmetric cyclopropanation reaction of olefins, [38][39][40][41][42] the most important being those in which the chiral auxiliary is linked to the olefin moiety via a glycosidic bond, making the final separation difficult.…”