Stereospecific functionalizations and transformations of secondary and tertiary boronic esters

Abstract

The formation of highly enantioenriched boronic esters through both stoichiometric and catalytic methods has received much attention over the past decade. Accordingly, the transformations of the boronic ester moiety into other functional groups is of considerable interest in synthesis. Specifically, transformations which retain the high enantioenrichment of the starting boronic ester, either through a stereoretentive or a stereoinvertive pathway, lead to the formation of new C-C, C-O, C-N, C-X, or C-H bonds at stereogenic centres. This feature article summarises the current state of the art in stereospecific transformations of both secondary and tertiary boronic esters into other functionalities and groups, whilst considering critically the transformations that are currently unattainable and would represent future advances to the field.

Enabling the Cross-Coupling of Tertiary Organoboron Nucleophiles through Radical-Mediated Alkyl Transfer

“…From the standpoint of organoboron coupling, this limitation actually serves to complement existing metal-free tertiary coupling work by Aggarwal and others, wherein tertiary alkyl pinacol boronates can be best coupled with electron-rich arene systems. 26 The current method also exhibits a notable absence of N -containing heteroaryl partners. In some ways, this failure of heteroaryl systems is mitigated by the successful implementation of tertiary alkyltrifluoroborates in Minisci processes, 27 but extension to other electrophilic sites on heteroaryl compounds would add significant value.…”

Alkyl‐C‐C‐Bindungsbildung durch Nickel/Photoredox‐Kreuzkupplung

“…[33] Es kçnnen andere bororganische Derivate in diesen Kupplungsreaktionen eingesetzt werden, wie durch ein Verfahren fürd ie Kreuzkupplung von Benzylboronsäurepinakolestern unter Strçmungsbedingungen von Ley et al deutlich wird. [37] [35] Dabei war das Hochdurchsatz-Screening [36] zur Identifizierung eines einzigartigen Liganden, 2,2,6,6-Tetramethylhep-tandion (TMHD), entscheidend, der die Kreuzkupplung dieser sterisch anspruchsvollen Radikalspezies ermçglichte.…”

Ligand‐Controlled Regiodivergent Enantioselective Rhodium‐Catalyzed Alkene Hydroboration

“…Avariety of subsequent transformations illustrate the potential utility of each product.Theenantioselectivepreparationofchiralboronicestersisof current interest due to the synthetic utility of these compounds in adiverse set of stereospecific transformations [1] and the growing appreciation that boronic acid derivatives may hold significant potential in medicinal chemistry. However,s mall differences in TADDOL-derived chiral monophosphite ligands can override this effect and direct rhodium-catalyzed hydroboration of baryl and b-heteroaryl methylidenes by pinacolborane to selectively produce either chiral primary or tertiary borated products.T he regiodivergent behavior is coupled with enantiodivergent addition of the borane.T he nature of the TADDOL backbone substituents and that of the phosphite moiety function synergistically to direct the sense and extent of regioselectivity and enantioinduction.…”