Reversal of Regioselectivity and Enhancement of Rates of Nitrile Oxide Cycloadditions through Transient Attachment of Dipolarophiles to Cyclodextrins
作者:Lorna Barr、Stephen F. Lincoln、Christopher J. Easton
DOI:10.1002/chem.200600627
日期:2006.11.15
4-tert-butylbenzonitrile oxide with acrylic acid, methacrylic acid, and crotonic acid is also altered by formation of the corresponding cyclodextrin esters, by factors of 500, >10, and >100, respectively. The rates of cycloaddition are also increased by up to 475 times, and in these cases the products of cycloaddition are readily released from the cyclodextrin through ester hydrolysis. Incorporating these
腈氧化物与单取代的亲脂性物质如丙酰胺的反应通常按比例提供80%或更多的3,5-二取代的环加合物。相比之下,6(A)-脱氧-6(A)-丙酰胺基-β-环糊精与4-叔丁基苄腈氧化物和4-苯基苄腈氧化物的反应可提供> 90%的溶液和约85%的相应3,4-二取代异恶唑分别。除了逆转区域选择性外,环糊精还增加了这些环加成的速率。对于环糊精优选的环加合物的生产,加速的程度高达三个数量级以上,但是甚至给出给出较不优选的区域异构体的反应速率也增加了。使用6(A)-脱氧-6(A)-丙酰胺基-β-环糊精,由于酰胺键不容易裂解,因此不容易将环加合物与环糊精分离。相比之下,4-叔丁基苄腈氧化物与丙烯酸,甲基丙烯酸和巴豆酸的环加成反应的区域选择性也通过形成相应的环糊精酯而改变,分别为500,> 10和> 100。环加成的速率也增加了多达475倍,在这些情况下,环加成的产物很容易通过酯水解从环糊精中释放出来。将这些过程