One-pot catalytic asymmetric borylation of unsaturated aldehyde-derived imines ; functionalisation to homoallylic boronate carboxylate ester derivatives.

The β-borylation reaction of α,β-unsaturated aldehyde-derived imines, formed in situ, has been studied using a one-pot methodology, as a route to β-boryl aldehydes. The instability of the β-boryl aldehydes meant that a derivatisation process was required to give more stable compounds. The best synthetic derivatisation pathway involved the synthesis of homoallylboronates using an in situ imine hydrolysis-Wittig olefination protocol, resulting in stable analogues from which enatiomeric excess could be readily measured. The resulting homoallylic boronate esters also provided an opportunity to introduce a second boryl unit in a stereoselective manner which will be useful for transformation into other functionalities leading to key building blocks for the synthesis of multi-functional, chiral compounds