FROM SUGARS TO CARBOCYCLES .2. 3-MEMBERED TO 7-MEMBERED RINGS FROM MANNOSE BY ADDITION OF 1,3-DITHIANE FOLLOWED BY INTRAMOLECULAR DISPLACEMENT REACTION

A new methodology for the conversion of sugars to three-, four-, six-, and seven-membered rings is presented. The sequence of transformation s is demonstrated with mannose (1) and involves addition of 2-lithio-1 ,3-dithiane to the acetonide 2 followed by elimination and reduction t o the 2-deoxy-dithiane 6. Starting from this intermediate, appropriate activation (tosylate, epoxide) and protection (acetonide, methyl ethe r) yields 8, 18, and 23, the starting materials for carbocyclization, which are converted by nucleophile displacement to the optically activ e cyclopropane 9, cyclobutane 19, cyclohexane 24, and cycloheptane 25, respectively. The cyclopropyl-1,3-dithane 9 can be desulfurized to th e cyclopropane 10.