Abstract
AbstractPhosphoramides and thiophosphoramides were prepared from optically pure C2‐symmetric 1,2‐diamines and were used as chiral organocatalysts in the asymmetric Michael additions of aldehydes and ketones to N‐substituted maleimides. The 1,2‐diphenylethane‐1,2‐diamine derived thiophosphoramide, which could be prepared in good yield in a one‐step procedure, was found to be more active and selective catalyst in the addition of aldehydes to various maleimide derivatives, when compared to sulfonamides having the same backbone. Products resulted in reactions of ketones with maleimides were also obtained in high yields and enantioselectivities.The thiophosphoramide derivative was also efficient in the asymmetric conjugate addition of carbonyl compounds to β‐nitrostyrene and in the reaction of nitromethane with α,β‐unsaturated ketones.Based on results obtained with (thio)phosphoramides in asymmetric additions to maleimides it was suggested that a weaker, more flexible hydrogen‐bonding of the rigid electrophile to the catalyst is responsible for the improved performance of these bifunctional organocatalysts, as compared with sulfonamides.magnified image
Highlights
Development of efficient chiral catalysts for the economical synthesis of optically pure compounds is a challenging task
Selection of the presented results was preceded by short optimizations with each maleimide derivative by changing the catalyst amount, reactant ratio and reaction time
The present study aimed at tuning the structure of chiral C2-symmetric diamines derived bifunctional organocatalysts for application in the asymmetric Michael addition of carbonyl compounds to maleimides by usingphosphoramide moieties as hydrogen-bond donor groups
Summary
Development of efficient chiral catalysts for the economical synthesis of optically pure compounds is a challenging task. A variety of chiral metal complexes and organocatalysts are available for the stereoselective preparation of optically enriched chemicals.[1,2] Fine-tuning the catalysts’ structure has paramount importance for improving their performances.[2] besides studies aimed at finding novel catalytic materials, research focused on the effect of structural modification of the catalysts are important. Asymmetric CÀ C bond-forming reactions have great significance in obtaining the structural complexity of the optically pure building blocks used in the pharmaceutical and fine chemical industry. Conjugate additions are privileged reactions, owing to the structural diversity of the employable donors and acceptors.[3,4] Various chiral metal complexes were found efficient in these reactions.[5] Since the beginning of the present century the explosive
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