Reaction of non-branched aldehyde, such as acetaldehyde or hexanal was also examined but it did not proceed. Transition state models of the reaction between isobutyraldehyde 7a and isatin 5bwere also examined by DFT calculations. After the structures of plausible transition state m odels without malonic acidwere fully optimized at the B3LYP/6-31G(d,p) level using PCM model (solvent ¼ethanol), we found that the energy difference was only 0.9 kcal/mol between calculated transition state models giving (S )- and (R)-isomers (see Supplementary data ), indicating that malonic acid would play a key role for both the acceleration of reactions and high stereoselectivities of the products.