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ABSTRACT: Enantiopure homoallylic boronate esters are versatile intermediates because the C–B bond in these com-pounds can be stereospecifically transformed into C–C, C–O and C–N bonds. Regio- and enantioselective synthesis of these precursors from 1,3-dienes has few precedents in the literature. We have identified reaction conditions and ligands for the synthesis of nearly enantiopure (er >97:3 to >99:1) homoallylic boronate esters via a rarely seen cobalt-catalyzed [4,3]-hydroboration of 1,3-dienes. Monosubstituted or 2,4-disubstituted linear dienes undergo highly efficient, regio- and enanti-oselective hydroboration with HBPin catalyzed by [(L*)Co]+[BARF]–, where L* is typically a chiral bis-phosphine ligand with a narrow bite angle. Several such ligands (examples: i-PrDuPhos, QuinoxP*, Duanphos and, BenzP*) that give high enantioselectivities for the [4,3]-hydroboration product have been identified. In addition, the equally challenging problem of regioselectivity is uniquely solved with a dibenzooxaphosphole ligand, (R,R)-MeO-BIBOP. A cationic cobalt(I) complex of this ligand is a very efficient (TON >960) catalyst, while providing excellent regioselectivities (rr >98:2) and enantioselectiv-ities (er >98:2) for a broad range of substrates. A detailed computational investigation of the reactions using Co-complexes from two widely different ligands (BenzP* and MeO-BIBOP) employing B3LYP-D3 density functional theory provides key insights into the mechanism and the origins of selectivities. The computational results are in full agreement with the exper-iments. For the complexes we have examined thus far, the relative stabilities of the diastereomeric diene-bound complexes [(L*)Co(4-diene)]+ leads to the initial diastereofacial selectivity, which in turn is retained in the subsequent steps, providing exceptional enantioselectivity for the reactions.