Aggarwal Varinder K, Grainger Richard S, Newton Gary K, Spargo Peter L, Hobson Adrian D, Adams Harry
School of Chemistry, Bristol University, Cantock's Close, Bristol, UK BS8 1TS.
Org Biomol Chem. 2003 Jun 7;1(11):1884-93. doi: 10.1039/b302834h.
The C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide, was found to react with a range of 3-oxidopyridinium betaines (bearing different substituents on nitrogen) in high yield and with total diastereoselectivity. A 2.3:1 mixture of regioisomers was formed with all of the 3-oxidopyridinium betaines but the ratio was found to change over prolonged periods of time due to reversibility of the minor regioisomer. 3-Oxidopyridinium betaines bearing methyl substituents at either the 2- or 6-position were also tested in the cycloaddition process. Improved regioselectivity (8:1) and again high diastereoselectivity were observed with the betaine having an additional substituent at the 2-position, but with betaines having a substituent in the 6-position although high regioselectivity was observed (9.9:1), the major isomer was formed with low diastereoselectivity (5.5:4.4). The origin of the regio- and diastereo-selectivity with all the betaines is discussed. Finally, the C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide was reacted with an oxidopyrylium betaine in moderate yield. Good regioselectivity and moderate diastereoselectivity were observed.
发现具有C2对称性的乙烯基亚砜，反式-2-亚甲基-1,3-二硫戊环1,3-二氧化物，能与一系列3-氧化吡啶鎓甜菜碱（氮上带有不同取代基）高产率且具有完全非对映选择性地反应。与所有3-氧化吡啶鎓甜菜碱反应均形成了2.3:1的区域异构体混合物，但由于次要区域异构体的可逆性，发现该比例会随时间延长而变化。还对在2-或6-位带有甲基取代基的3-氧化吡啶鎓甜菜碱进行了环加成反应测试。对于在2-位有额外取代基的甜菜碱，观察到区域选择性提高（8:1）且再次具有高非对映选择性，但对于在6-位有取代基的甜菜碱，尽管观察到高区域选择性（9.9:1），但主要异构体的形成具有低非对映选择性（5.5:4.4）。讨论了所有甜菜碱的区域和非对映选择性的起源。最后，使具有C2对称性的乙烯基亚砜，反式-2-亚甲基-1,3-二硫戊环1,3-二氧化物与氧化吡啶鎓甜菜碱反应，产率适中。观察到良好的区域选择性和适中的非对映选择性。
