Regio‐ and Stereoselective Homologation of 1,2‐Bis(Boronic Esters): Stereocontrolled Synthesis of 1,3‐Diols and Sch 725674
作者:Alexander Fawcett、Dominik Nitsch、Muhammad Ali、Joseph M. Bateman、Eddie L. Myers、Varinder K. Aggarwal
DOI:10.1002/anie.201608406
日期:2016.11.14
1,2-Bis(boronic esters), derived from the enantioselective diboration of terminal alkenes, can be selectively homologated at the primary boronic ester by using enantioenriched primary/secondary lithiated carbamates or benzoates to give 1,3-bis(boronic esters), which can be subsequently oxidized to the corresponding secondary-secondary and secondary-tertiary 1,3-diols with full stereocontrol. The transformation
Stereoselectivity in the Rhodium-Catalysed Reductions of Non-Conjugated Dienes
作者:Bao Nguyen、John M. Brown
DOI:10.1002/adsc.200900013
日期:2009.6
Abstractmagnified imageThe stereochemical course of rhodium‐catalysed addition of hydrogen and catecholborane to bicyclo[2.2.1]heptadiene, and of hydrogen to a range of cyclic dienes has been analysed. For hydroboration, the overall catalytic reaction possesses exo‐selectivity, but the initial step is endo‐selective. For hydrogenation (deuteration), the first step may occur with either exo‐ or endo‐ selectivity, depending on the structure of the diene. This enables a distinction to be made between pathways involving prior dissociation of the diene, and direct addition to the complexed diene without full dissociation. The relative ease of hydrogenation of the first and second double bonds varies markedly with reactant structure, and also depends on the choice of catalyst ligands. For dicyclopentadiene, hydrogenation of the cyclopentene double bond is accompanied by rapid alkene isomerisation, as revealed by deuterium addition. The asymmetric hydrogenation of acyclic skipped meso‐dienes is reported, demonstrating control of relative rates of the two sequential steps, with ees of up to 53% after the first reduction.