AlkeneAdditions3

AlkeneAdditions3 - Hydroboration-Oxidation 2 step process...

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1 2-48 Hydroboration Hydroboration -Oxidation -Oxidation ± 2 step process ± overall hydration - ANTI-MARKOVNIKOV ² source of R 2 BH usually B 2 H 6 OR BH 3 •THF ² no carbocation intermediate - no rearrangements CC hydroboration + CCB R 2 H CCO H H oxidation HOOH OH HB R 2 + + R 2 H ROH B(OH) 4 + + 2-49 Mechanism: 1. Mechanism: 1. Hydroboration Hydroboration ² Stereoselective: SYN addition - BR 2 and H add to same face of double bond ² Regioselective: ANTI-Markovnikov boron adds to least substituted carbon (sterics AND stability) H 3 CHC CH 2 + HC CH 2 R 2 HC CH 2 R 2 pi complex H H 2 R 2 4-center transition state H 3 C H 3 C HC CH 2 R 2 H 3 C + H 3 C BR 2 H
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2 2-50 Mechanism: 2. Oxidation Mechanism: 2. Oxidation ± Stereoselective: retention of configuration HOO + CC HO–B(OR) 2 + H 3 C H H BR 2 H 3 CH HB R 2 O O H H 3 H BR 2 O OH 2 OOH H 3 H B(OR) 2 O 3 OH H 3 H B(OR) 2 O 2 OH OH H 3 H OH 3 OH H O H
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3 2-51 Oxymercuration Oxymercuration -Demercuration Demercuration ± overall Markovnikov hydration without rearrangement CC HO Hg HO H H 2 O Hg(OCCH 3 ) 2 O OCCH 3 O HO Hg OCCH
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AlkeneAdditions3 - Hydroboration-Oxidation 2 step process...

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