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.
Enantioselective Organocatalyzed Bromolactonizations: Applications in Natural Product Synthesis
作者:Marius Aursnes、Jørn E. Tungen、Trond V. Hansen
DOI:10.1021/acs.joc.6b01375
日期:2016.9.16
The best catalyst enabled the cyclization of several 5-arylhex-5-enoic acids into the corresponding bromolactones with up to 96% ee and in high to excellent chemical yields. The reported catalysts are prepared in a straightforward manner in two steps from dimethyl squarate. The utility of the developed protocol was demonstrated in highly enantioselective syntheses of the sesquiterpenoids (−)-gossoronol