Ch 10 and 11 Chemistry of alcohols and thiols

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Unformatted text preview: w pulls slightly and is easy to control by maintaining a firm grip. Cutting from the underside of a branch requires you to cut • • • • • Reactions of 1,2-Diols: Periodic Acid Cleavage!   General Reaction:! C C O O H2O2 HIO4 OsO4 OH + OH O Vicinal Diol! HIO4 = ! O I OH O Periodic Acid!   Characteristics:! •  only 1,2-diols (a.k.a. vicinal diols or glycols) are cleaved by HIO4! •  the products are the same aldehydes and/or ketones that would result from ozonolysis with O3! 10-42! Mechanism of Periodic Acid Cleavage! Involves a cyclic periodate ester intermediate! CH3 OH OH O CH3 HIO4 + HIO3! O O O H CH3 I OH O O •  This reaction is a powerful method for analyzing sugar structures and activating antibodies for coupling to drugs to create targeted pharmaceuticals.! 10-43! Synthesis Problem!   How would you synthesize! OH OH HO OH ! ! ! !from ! ! ! !?! 10-44! Reactions of 1,2-Diols: Cyclic Acetal Formation!   General Reaction:! ! R HO C O OH Acid Catalysis R'   O R + H2O! C R' O Characteristics:! •  common method to protect a carbonyl prior to exposure to a powerful nucleophile or base to prevent reaction at the carbonyl carbon! •  this is an equilibrium process, so carbonyl protection and deprotection are driven by biasing the equilibrium in one direction or the other! 10-45! Reactions of 1,2-Diols: Cyclic Acetal Formation!   Mechanism:! HO R R Protonation O C R C OH C OH O R' R' OH Addition HO R' H H HO R OH H HO R Deprotonation R OH Protonation C C ROH R' Loss of H2O C C O O R' R' HO R O O O HO R' H H HO R O Addition C R O R' R' ROH O R C C O Deprotonation R' O 10-46! Reactions of 1,2-Diols: Pinacol Rearrangement!   General Reaction:! OH OH OH O CH2 H3C !   C C CH3 H3C C C C + CH3 C CH3 H3C CH3 CH3 CH3 Mechanism:! CH3 H OH H3C CH3 C C CH3 H O OH C CH3 CH3 ! ! ! H H3C C CH3 CH3 ! ! ! Loss of Water C CH3 CH2 C C CH3 CH3 CH3 OH H C OH H3C Protonation OH H3C OH2 CH3 OH O H H Deprotonation CH2 H3C CH3 C C CH3 CH3 Methyl Shift H O C O H CH3 H H3C C CH3 CH3 O CH3 C Deprotonation H3C C CH3 CH3 10-47! Epoxide Synthesis: Epoxidation of Alkenes!   General Reaction:! O C C + RCO3H 1-3hr C C + RCO2H peroxyacid! Epoxide !   Characteristics: ! •  •  •  •  (valuable synthetic intermediate for acid- or base-catalyzed oxirane ring opening) ! syn addition of oxygen to the C=C bond olefin stereochemistry retained in epoxide (oxirane) product oxygen atom originates from peroxy acid rate increases with increasing electron donation by C=C substituents Relative Rates of Epoxidation CH2=CH2 1.0 CH3CH=CH2 22 (CH3)2C=CH2 484 •  short reaction times needed (i.e., RCO2H addition to epoxide competes at long reaction times) 10-48! Synthesis Of Epoxides!   Peroxy Acid Types! O O Cl R= H, CH3, Ph, MCPBA OH MCPBA! O R OH O !   Mechanism:! R H O R O O ! O H H C R 1 O H O O H C H C R C R R 1 C + RCO2H! 2 C 2 R 1 R 2 10-49! Alkene Epoxidation Is Not Facially Selective! 10-50! K. Barry Sharpless (Stanford, 1980): 2001 Nobel Prize in Chemistry! 10-51!...
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This note was uploaded on 01/27/2014 for the course BIOL 241 taught by Professor Henrychang during the Winter '10 term at Purdue University-West Lafayette.

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