Experimental and theoretical studies on stereo- and regioselectivity in intramolecular nitrone-alkene cycloaddition of Hept-6-enoses derived from carbohydrates
Experimental and theoretical studies on stereo- and regioselectivity in intramolecular nitrone-alkene cycloaddition of Hept-6-enoses derived from carbohydrates
复制标题
DOI：
10.1021/jo060348y
复制
发表时间：
2006-04-14
影响因子：
3.6
通讯作者：
Yamada, T
中科院分区：
文献类型：
--
作者：
Shing, TKM;Wong, AWF;Yamada, T
报道了取代基的立体化学性质和封隔基团对分子内硝基-烯烃环加成反应的区域选择性和立体选择性的影响。以d -核糖和d -阿拉伯糖为原料分别制备了含有2,3- o-异丙基阻断基团的l -核糖-庚-6-烯糖12和d -羟基-庚-6-烯糖15，以及含有2,3- o-反式双缩醛阻断基团的l -木糖-庚-6-烯糖23和d -阿拉伯糖-庚-6-烯糖30。与n -烷基羟胺，内酯12和15进行INAC反应得到顺式融合异恶唑烷，而内酯23和30得到顺式、反融合异恶唑烷（环己醇）和桥接异恶唑烷（环庚醇）的混合物。首次以未支链糖衍生物23和30为原料，以2,3-0-反式双缩醛保护基团，通过INAC环化内端模式合成了桥接的双环[4.2.1]异恶唑烷（环庚醇）。根据计算得到的过渡态能，对这些反应的立体化学结果进行了合理化。目前的INAC表现出轻微的温度依赖性，但明显的溶剂依赖性。对于内酯23和内酯30，在2-丙醇中进行INAC反应可以得到最佳的熔融异恶唑烷（环己醇）收率，而在二氯甲烷中进行INAC反应可以得到最佳的桥接异恶唑烷（环庚醇）收率。
The effect of blocking groups and stereochemistry of the substituents on the regio- and stereoselectivity in intramolecular nitrone-alkene cycloaddition (INAC) of hept-6-enoses are reported. L-ribo-Hept-6-enose 12 and D-lyxo-hept-6-enose 15, both containing a 2,3-O-isopropylidene blocking group, and L-xylo-hept-6-enose 23 and D-arabino-hept-6-enose 30, both with a 2,3-O-trans-diacetal blocking group, were prepared from D-ribose and D-arabinose, respectively. With N-alkyl hydroxylamine, lactols 12 and 15 underwent an INAC reaction to give cis-fused isoxazolidines exclusively whereas lactols 23 and 30 gave a mixture of cis-, trans-fused isoxazolidines (cyclohexanols) and bridged isoxazolidines (cycloheptanols). With the 2,3-0-trans-diacetal protecting group, the bridged bicyclo[4.2.1]isoxazolidines (cycloheptanols), via the endo mode of INAC cyclization, were synthesized for the first time from Unbranched sugar derivatives 23 and 30. The stereochemical outcomes of these reactions were rationalized on the basis of transition state energies obtained by computation. The present INAC showed trivial temperature, but significant solvent dependence. For lactols 23 and 30, performing the INAC in 2-propanol gave the best yields of fused isoxazolidines (cyclohexanols) whereas in dichloromethane afforded the best yields of bridged isoxazolidines (cycloheptanols).