A new ring closure approach to enantiopure 3,6-dihydro-2H-pyrans: stereodivergent access to carbohydrate mimetics.

A set of enantiopure carbohydrate mimetics has been synthesized via Lewis acid promoted cyclization of 1,3-dioxolanyl-substituted enol ethers as a crucial new step providing highly functionalized 3,6-dihydro-2H-pyran derivatives. The flexible approach starting from glyceraldehyde-derived nitrone is comprised of only six simple steps smoothly allowing synthetic modifications at the different stages of the sequence. All reactions proceeded with good to excellent stereocontrol and can be performed with either of the two enantiomers.