| Popis: |
Methyl 4,6-O-benzylidene-3-deoxy-3-C-ethyl-α- D -ribo-hexopyranosid-2-ulose (2) reacts with lithium aluminium hydride, methylmagnesium iodide, and phenylmagnesium bromide to give products having only the allo configuration. The C-3 epimer of 2, methyl 4,6-O-benzylidene-3-deoxy-3-C-ethyl-α- D -arabino-hexopyranosid-2-ulose (7), reacts with lithium aluminium hydride to give only a product having a gluco configuration. With methylmagnesium iodide and phenylmagnesium bromide, 7 gives products having gluco and manno configurations. The 2-C-methyl-glucopyranoside preponderates in the former reaction, and the 2-C-phenyl-mannopyranoside is the major product in the latter reaction. The reaction between 2 and diazomethane gives a spiro-epoxide having the allo configuration as the major product (i.e., the same configuration as the 2-MeMgI reaction product), whereas the 7-diazomethane reaction gives a spiro-epoxide having the manno configuration (i.e., the same configuration as the minor product from the 7-MeMgI reaction) as the major product. With the thionyl chloride-pyridine reagent, 3-deoxy-3-C-ethyl-2-C-methyl-α- D -hexopyranosides are dehydrated endocyclically when H-3 and HO-2 are antiparallel and exocyclically when H-3 and HO-2 have a gauche relationship. |
