Enantioenriched BoronC,N‐Chelates via Chirality Transfer

Abstract

AbstractMolecules stereogenic only at tetrahedral boron atoms show great promise for applications, for example as chiroptical materials, but are scarcely investigated due to their synthetic challenge. Hence, this study reports a two‐step synthesis of enantioenriched boronC,N‐chelates. First, the diastereoselective complexation of alkyl/aryl borinates with chiral aminoalcohols furnished boron stereogenic heterocycles in up to 86 % yield and d.r. >98 : 2. Treatment of theseO,N‐complexes with chelate nucleophiles was surmised to transfer the stereoinformation via the ate‐complex into theC,N‐products. This chirality transfer succeeded by substitution of theO,N‐chelates with lithiated phenyl pyridine to give boron stereogenicC,N‐chelates in up to 84 % yield and e.r. up to 97 : 3. The chiral aminoalcohol ligands could be recovered after isolation of theC,N‐chelates. The chirality transfer tolerated alkyl, alkynyl and (hetero‐)aryl moieties at boron and could be further extended by post‐modification: transformations such as catalytic hydrogenations or sequential deprotonation/electrophilic trapping were feasible while maintaining the stereochemical integrity of theC,N‐chelates. Structural aspects of the boron chelates were studied by variable temperature NMR and X‐ray diffraction.