TASTE · New Transformations of Secondary Alkylboronic Esters

The properties of organic molecules are defined by their shape andfunctionality. However, the creation of such molecules with controlover both of these features is highly challenging. This proposaldescribes novel methodology for simultaneous C-C bond formation with controlover shape (stereochemistry). In particular it focuseson the stereoselective replacement of boron (which is easy tointroduce) to halides and other heteroatoms, and new ways forcross-coupling to aromatics without the need for transition metals.In order to promote the electrophilic halogenation of a boronicester, we envisaged the reaction of boronate complex with a halogen electrophile. In preliminary experiments such processes have alreadybeen found to be viable and occur with complete stereoinversion.Through tuning the nature of the aryl lithium one could envisageselective halogenation of a broad range of substrates, giving accessto a myriad of stereodefined secondary alkyl halides, includingfluorides. Moreover, alcohols, amines derivatives, thioethers andselenoethers could all be accessible by the reaction of these newactivated boronic ester ate complexes with suitable electrophiles.The final part will focus on the (transition metal-free) crosscoupling of secondary alkylboronic esters. We present a conceptually newapproach to this challenging problem by considering the reaction of asecondary boronic ester with an aryl lithium reagent. Following atecomplex formation, one-electron oxidation would result indearomatization leading to a radical cation which would trigger a1,2-migration/rearomatization sequence. High stereointegrity can beexpected for such a process from the stereospecificity of the1,2-sigmatropic rearrangement. Preliminary results have shown thatthe concept is again viable but needs substantial optimization. This methodology will be applied tochallenges in synthesis.""