CONFORMATIONAL STUDIES OF CHIRAL ALPHA,BETA-UNSATURATED ALDEHYDES

The conformational profiles for chiral alpha,beta-unsaturated aldehydes have been studied by a combination of ab initio MO methods and the variable-temperature MMR technique. The s-trans rotational isomer around the C-sp2-C-sp2 single bond is more stable than the s-cis conformer by similar to 500 cal/mol in chloroform. This difference is 950 cal/mol according to ab initio calculations at the MP2/6-31G* level of theory. The silyl ethers, 3a-d, prefer the C-O eclipsed form while the methyl ethers, 6a-d, favor the C-H eclipsed conformation for rotations around the C-sp3-C-sp2 bond.