Binding the anion: A highly enantioselectiveiodolactonization of 5‐hexenoic acids has been achieved using a tertiary aminourea‐catalyst (see scheme). The use of catalytic iodine in this process is critical to enhancing both the reactivity and enantioselectivity of the stoichiometric I+ source. The mechanism is proposed to involve binding of an iodonium imidate intermediate by the H‐bond donor catalyst
结合阴离子:使用叔氨基脲催化剂实现了 5-己烯酸的高度对映选择性碘内酯化(参见方案)。在该过程中使用催化碘对于提高化学计量 I +源的反应性和对映选择性至关重要。该机制被认为涉及通过氢键供体催化剂结合亚胺酸碘鎓中间体。
作者:Jørn E. Tungen、Jens M. J. Nolsøe、Trond V. Hansen
DOI:10.1021/ol302798g
日期:2012.12.7
Asymmetric iodolactonization of gamma- and delta-unsaturated carboxylic acids has been explored in the presence of six different chiral organocatalysts 5-8. The catalyst 6b was found to facilitate the cyclization of 5-arylhex-5-enoic acids 1 to the corresponding iodolactones 2 with up to 96% ee. By this protocol, unsaturated carboxylic acids are converted enantioselectively to synthetically useful delta-lactones in high yields using commercially available NIS. Apparently, both hydrogen bonding and aryl/aryl interactions are important for efficient stereodifferentiation.