12 research outputs found
Enantiospecific sp(2)-sp(3) coupling of secondary and tertiary boronic esters
The cross-coupling of boronic acids and related derivatives with spÂČ electrophiles (the SuzukiâMiyaura reaction) is one of the most powerful CâC bond formation reactions in synthesis, with applications that span pharmaceuticals, agrochemicals and high-tech materials. Despite the breadth of its utility, the scope of this Nobel prize-winning reaction is rather limited when applied to aliphatic boronic esters. Primary organoboron reagents work well, but secondary and tertiary boronic esters do not (apart from a few specific and isolated examples). Through an alternative strategy, which does not involve using transition metals, we have discovered that enantioenriched secondary and tertiary boronic esters can be coupled to electron-rich aromatics with essentially complete enantiospecificity. As the enantioenriched boronic esters are easily accessible, this reaction should find considerable application, particularly in the pharmaceutical industry where there is growing awareness of the importance of, and greater clinical success in, creating biomolecules with three-dimensional architectures
Asymmetric Synthesis of Tertiary Alcohols and Thiols via Nonstabilized Tertiary α-Oxy- and α-Thio-Substituted Organolithium Species
Nonstabilized αâOâsubstituted tertiary organolithium species are difficult to generate, and the αâSâsubstituted analogues are configurationally unstable. We now report that they can both be generated easily and trapped with a range of electrophiles with high enantioselectivity, providing ready access to a range of enantioenriched tertiary alcohols and thiols. The configurational stability of the αâSâorganolithium species was enhanced by using a less coordinating solvent and short reaction times
Recent Advances in Catalysis Using Organoborane-Mediated Hydride Abstraction
C-H functionalization is widely regarded as an important area in the development of synthetic methodology, enabling the design of more time- and atom-efficient syntheses. The ability of electron-deficient organoboranes to mediate hydride abstraction from α-amino C?H bonds is therefore of great interest, as the reactive iminium and hydridoborate moieties generated are able to participate in a range of synthetically useful transformations. In this review update, we cover the recent advances made in organoborane mediated hydride abstraction, with particular focus on the catalytic applications of electron deficient boranes for α- or ÎČ- functionalization, α,ÎČ-difunctionalization, and the dehydrogenation of amines.</p
Stereospecific conversion of alcohols into pinacol boronic esters using lithiationâborylation methodology with pinacolborane
The synthesis of primary and secondary pinacol boronic esters via
lithiationâborylation of carbamates and benzoates with pinacolborane is described. This new protocol enables the highly selective
synthesis of enantioenriched and geometrically defined boronic esters
that cannot otherwise be accessed by alternative methodologies
Assembly-line synthesis of organic molecules with tailored shapes
International audienceMolecular âassembly linesâ, in which organic molecules undergo iterative processes such as chain elongation and functional group manipulation, are found in many natural systems, including polyketide biosynthesis. Here we report the creation of such an assembly line using the iterative, reagent-controlled homologation of a boronic ester. This process relies on the reactivity of α-lithioethyl tri-isopropylbenzoate, which inserts into carbonâboron bonds with exceptionally high fidelity and stereocontrol; each chain-extension step generates a new boronic ester, which is immediately ready for further homologation. We used this method to generate organic molecules that contain ten contiguous, stereochemically defined methyl groups. Several stereoisomers were synthesized and shown to adopt different shapesâhelical or linearâdepending on the stereochemistry of the methyl groups. This work should facilitate the rational design of molecules with predictable shapes, which could have an impact in areas of molecular sciences in which bespoke molecules are required