| In this thesis, a review regarding the syntheses of medium-membered cyclic ethers from 1965 to September 1997 is presented. It delineated the progress of the synthetic methodologies.; An improved silica gel-supported periodate reagent in powder form for the efficient and facile preparation of aldehydes in high yield from 1,2-diols has been described.; A new, practical, efficient, and diastereoselective synthetic route for the construction of 8- to 12-membered cyclic ethers (e.g. compounds 233 to 236, 246, 253, 254, and 260) via INOC reactions is described. A novel type of isoxazoline compounds containing a bridge head C=N bond in a medium-sized ring (e.g. 9-, 10-, and 11-membered rings) via INOC reactions was obtained.; The use of INAC reactions of O-allyl-nitrones derived from monosaccharides to regio- and diastereo-selective construction of 6- and 7-membered O-heterocycles was developed. By examining the stereoselectivity of the INAC reactions, we have demonstrated for the first time that the stereochemical outcome the INAC reactions of nitrones derived from 3-O-allyl-monosaccharides to exo-cycloaddition products (269, 273, 277, 280 , 283, 284, 287, 288, 291, 292, and 301) is dependent only on the vinylogous anomeric effect.; Eight different aldehydes (356, 358, 371, 373, 384, 386, 396 , and 398) were prepared in order to examine the ring-selectively and stereo-control via INAC based on the effect of the presence of electron withdrawing group. Conformational analyses for the exo-products (360--363, 375, 377, 378 , 388, 390, 400, and 402), showed that the vinylogous anomeric effect leads to the stereoselective formation of only one major tetrahydropyran (THP) compound. When the anomeric effect is in piC=C→sigma*C---O donation, cis-fused THPs predominated; When the anomeric effect is in sigma C---O→pi*C=N donation, trans-fused THPs were obtained.; On the diastereoselective construction of five-membered carbocycles via INAC reactions, we first recognized that the cycloaddition of the nitrone 419 can be catalyzed by palladium. The mechanism via a palladium complex was proposed. By adding sodium ion, the carbocycle 423, which is a key intermediate for synthesis of a number of natural products, has been regio- and diastereo- selectively synthesized.; By the syntheses of four cyclobutane derivatives (446, 448, 450, and 452) for exploring [2 + 2] intromolecular enamines cycloaddition, we found that the thermal [pi 2s + pi2a] cycloaddition via concerted process was sterically controlled in addition to the conditions of having electron-rich and electron-poor alkenes. Otherwise, a competing two-step zwitterion mechanism occurred. |
