Hydroboration achiral olefins

Catalytic Asymmetric Hydroboration. The hydroboration of olefins with catecholborane (an achiral hydroborating agent) is cataly2ed by cationic rhodium complexes with enantiomericaHy pure phosphines, eg, [Rh(cod)2]BE4BINAP, where cod is 1,5-cyclooctadiene and BINAP is... 

The uncatalyzed hydroboration-oxidation of an alkene usually affords the //-Markovnikov product while the catalyzed version can be induced to produce either Markovnikov or /z/z-Markovnikov products. The regioselectivity obtained with a catalyst has been shown to depend on the ligands attached to the metal and also on the steric and electronic properties of the reacting alkene.69 In the case of monosubstituted alkenes (except for vinylarenes), the anti-Markovnikov alcohol is obtained as the major product in either the presence or absence of a metal catalyst. However, the difference is that the metal-catalyzed reaction with catecholborane proceeds to completion within minutes at room temperature, while extended heating at 90 °C is required for the uncatalyzed transformation.60 It should be noted that there is a reversal of regioselectivity from Markovnikov B-H addition in unfunctionalized terminal olefins to the anti-Markovnikov manner in monosubstituted perfluoroalkenes, both in the achiral and chiral versions.70,71... 

Complexes of rhodium compounds with enantiomerically pure phosphines facilitate enantiose-lective hydroboration of prostereogenic olefins with 1,3,2-benzodioxaborole (catecholboranc), an achiral hydroborating agent. The reactions are carried out using a 1 1.1 -1.2 molar ratio of the olefin and catecholboranc in the presence of 1 mol % of the catalyst which is generated in situ111"113. The following catalysts are used ... 

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