Horton D, Priebe W, Sznaidman M
Department of Chemistry, Ohio State University, Columbus 43210.
Carbohydr Res. 1990 Sep 19;205:71-86. doi: 10.1016/0008-6215(90)80129-q.
Exclusive trans-addition is observed in the iodoalkoxylation of the 6-membered cyclic enol ethers 3,4-di-O-acetyl-L-rhamnal (1), 3,4-di-O-acetyl-L-fucal (2), and related glycal derivatives. The main products from 1 and from 3,4,6-tri-O-acetyl-D-glucal (3) thus had the alpha-manno configuration. Similarly, alpha-talo products were obtained from 2 in 87-93% yield. The product distribution is not affected by the electronegativity of the 5-substituent. It is concluded that steric factors in the glycal and the nucleophile affect only the step of trans-diaxial opening of the intermediate iodonium ion. Enhanced yields of the desired trans-diaxial products were observed in reactions of glycals having the lyxo configuration when the reactions were conducted in tetrahydrofuran or methanol.
在六元环烯醇醚3,4-二-O-乙酰基-L-鼠李糖醛（1）、3,4-二-O-乙酰基-L-岩藻糖醛（2）及相关糖烯衍生物的碘烷氧基化反应中观察到了专一的反式加成。因此，1以及3,4,6-三-O-乙酰基-D-葡萄糖烯（3）的主要产物具有α-甘露糖构型。类似地，从2以87 - 93%的产率得到了α-塔罗糖产物。产物分布不受5-取代基电负性的影响。得出的结论是，糖烯和亲核试剂中的空间因素仅影响中间体碘鎓离子的反式双轴开环步骤。当反应在四氢呋喃或甲醇中进行时，在具有lyxo构型的糖烯的反应中观察到所需反式双轴产物的产率提高。
