Iodolactonization of 4,5-disubstituted 2-(trimethylsilylmethyl)- and 2-methyl-penta-2,4-dienoic acids was studied. The latter afforded the corresponding iodolactone in good yield by treatment with I2 in MeCN. Iodolactone was also obtained by treatment with I2/NaHCO3/CHCl3/H2O in the presence of cerium(IV) salt as an additive. It was found that protolactonization proceeds by the aid of the trimethylsilyl group, while it prevents iodolactonization.
Synthesis of (E)-α,β-unsaturated esters in high yields and with total stereoselectivity is achieved from α-halo-β-hydroxy esters promoted by catalytic amounts of SmI2. The starting compounds were easily prepared from α-halo esters and aldehydes as a mixture of stereoisomers. A mechanism is proposed to explain this samarium(II)-promoted catalytic β-elimination reaction.
Synthesis and biological activity of enantiomeric pairs of 5-[(E)-cycloalk-2-enylidenemethyl]thiolactomycin congeners
作者:Kohei Ohata、Shiro Terashima
DOI:10.1016/j.bmcl.2008.08.103
日期:2008.10
The title congeners were synthesized by employing our efficient synthetic route previously explored for preparing enantiomeric pairs of thiolactomycin and its 3-demethyl derivative. While all the synthesized congeners lacked in vitro antibacterial activity, some of the congeners bearing an (E)-cyclohept-2-enylidenemethyl or an (E)-cyclooct-2-enylidenemethyl group were found to exhibit more potent type