Preparation of dioxolane-type fluoren-9-ylidene acetals of carbohydrates and their hydrogenolysis with AlClH2 to give axial fluoren-9-yl ethers

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cis-Hydroxyl groups of hexopyranosides reacted with 9,9-dichlorofluorene to give fluoren-9-ylidene acetals, hydrogenolysis of which with AlClH2 gave derivatives with axial fluren-9-yl ether and equatorial hydroxyl groups. 1,6-Anhydro-2,3-O-fluoren-9-ylidene-β-d-mannopyranose (9) was an exception which gave a 2:3 mixture of 2- and 3-fluoren-9-yl ethers because of the marked distortion of the pyranose ring. The fluoren-9-yl ether groups could be removed easily by catalytic hydrogenation or by hydrogenolysis with the Lewis acid-type mixed hydride AlCl2H.