The Ireland ester enolate Claisen rearrangement gives rise to Z-trisubstituted alkenes via heteroatom mediated substrate pre-organization prior to rearrangement.
A Chelation-Controlled Ester Enolate Claisen Rearrangement
摘要:
The Ireland ester enolate Claisen rearrangement gives rise to Z-trisubstituted alkenes due to heteroatom-enforced control over the conformation of the transition state. An oxygen-bearing functional group at the tertiary carbinol center, which can coordinate to the enolate metal via a seven-membered chelated transition state, provides the control element to explain the selectivity. alpha,beta-Disubstituted unsaturated carboxylic acids are also formed with high diastereoselectivity.
[reaction: see text] The rhodium(I)-catalyzed methylenation of ketones using trimethylsilyldiazomethane proceeds to give the corresponding alkenes in good yields (60-97%). The use of an excess of 2-propanol and 1,4-dioxane as a solvent were instrumental to obtain the desired alkenes in high yields. Superior results were achieved with the rhodium(I)-catalyzed methylenation in comparison with the standard