Fructose cyclic hemiacetal formation

The sugar fructose is an isomer of glucose. Like glucose, fructose forms a cyclic hemiacetal, but in this case the ring is five membered rather than six membered. Show the structure for the hemiacetal formed from fructose and show a mechanism for its formation in acidic solution. 

To summarize the mechanistic and structural studies with hex-2-uloses and 2-C-(hydroxymethyl)pentoses performed under the conditions of the Bflik reaction, the following conclusion can be made. Molybdic acid catalyzes two types of interconversions between the sugars shown in Scheme 13. D-Fructose (17), d-sorbose (21) and D-tagatose (29) when treated with the catalyst are subjected to highly stereospecific carbon-skeleton rearrangements to produce thermodynamic equilibrium mixtures with the respective 2-C-(hydroxymethyl)-D-ribose (D-hamamelose, 20), 2-C-(hydroxymethyl)-D-lyxose (30), and 2-C-(hydroxymethyl)-D-xylose (31). (For simplicity, all the sugars are represented in their acyclic non-hydrated forms in spite of which some of their interconversions proceed in the acyclic hydrated structures, while others proceed in cyclic hemiacetal ones. All of the interconversion relationships are schematically represented in the d series, despite the fact that some of them were experimentally performed with the L series.) Probably because of extensive formation of unproductive com-... 

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