Chem 232 Lecture 12 - UIC Department of Chemistry - University of ...
Chem 232 Lecture 12 - UIC Department of Chemistry - University of ... Chem 232 Lecture 12 - UIC Department of Chemistry - University of ...
Regioselectivity DeterminedDuring HydroborationO O BH 2O OHcompare to . . .OH 2 SO 4OOSO 3 HH 3 B•THF H 2 O 2 /OH – OH 2 O/heatOH• boron atom is added to least substituted carbonatom, hydrogen atom is added to most substituted• after oxidation, gives the least substituted product• opposite regioselectivity of Markovnikov additionUniversity of IllinoisUICat Chicago CHEM 232, Spring 2010Slide 12Lecture 12: February 1812
Mechanism of HydroborationH 2 BHCH 3H 2 BHCH 3 CH 3CH 3H 2 BCH 3Why this regioselectivity?H 2 BnotUniversity of Illinois• Syn Addition: B and H atoms add to same side(face) of C-C double bond at same time• hydride (H:) adds to most substituted carbon• boron adds to least substituted carbon• this is NOT a PROTONATIONUICat Chicago CHEM 232, Spring 2010Slide 13Lecture 12: February 18Note that although the borane generated upon monohydroboration of methylcyclopentene is itselftrans-substituted, the hydroboration remains a syn-addition. In other words, it is the BH2 groupand beta-hydrogen on the carbon bearing the methyl group which are in a syn relationship.13
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Regioselectivity DeterminedDuring HydroborationO O BH 2O OHcompare to . . .OH 2 SO 4OOSO 3 HH 3 B•THF H 2 O 2 /OH – OH 2 O/heatOH• boron atom is added to least substituted carbonatom, hydrogen atom is added to most substituted• after oxidation, gives the least substituted product• opposite regioselectivity <strong>of</strong> Markovnikov addition<strong>University</strong> <strong>of</strong> Illinois<strong>UIC</strong>at Chicago CHEM <strong>232</strong>, Spring 2010Slide <strong>12</strong><strong>Lecture</strong> <strong>12</strong>: February 18<strong>12</strong>
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