The 1,6-anhydro-2,3-dideoxy-B-D-erythro-/-threo-hex-2-enopyranoses 7-12 are valuable synthons for the preparation of structurally diverse natural productP, because (a) the rigid [3.2. llbicyclic framework facilitates highly stereo-and regio-selective reactionP, (b) each contains a reactive double bond and allylic hydroxyl group, (c) the locked conformation facilitates the generation of stereo centres which are opposite in configuration to those generated from compounds with conventional "C, conformations, and (d) the internal acetal reduces the number of protecting groups that are required. Compounds 7-12 have been prepared by low-yielding, multi-step procedures starting from 1,6-anhydrogalactopyranoseksa.
We now report on a new, general, and efficient route to the 1,6-anhydro-2,3dideoxy-/I-D-erythro-(7-9) and -/I-D-fhreo-hex-2-enopyranoses (10-12) from the easily accessible 3,4-di-O-substituted glycals l-6, which involves a novel "intramolecular" Ferrier reactior?.
Thus, 3,4-di-O-acetyl-(l), 3,4-di-O-benzoyl-(2), and 3,4-di-0-benzyl-D-glucal (3) were each reacted in dry dichloromethane at 0" with a catalytic amount of boron trifluoride etherate to give 4-O