Rearrangements CH3 CH3 CH3 CH CH.50%HSO CH3-C-CH-CH3 CH3 OH CH3 Rearrangement: CH3 CH3 CH3 CHg-C-CH-CH3 CH3-C-CH-CH3 →CH3-C—CH-CH3 CH3 CH3 OH CH3 2°，less stable 3°，more stable 2,3-dimethyl-2-butanol (major product) Rearrangements can occur when there are carbocation intermediates. A methyl shift after protonation will produce the more stable tertiary carbocation. Chapter8 16
Chapter 8 16 Rearrangements CH3 C CH CH2 CH3 CH3 CH3 C CH CH3 CH3 OH CH3 50% H2SO4 • Rearrangements can occur when there are carbocation intermediates. • A methyl shift after protonation will produce the more stable tertiary carbocation. 2,3-dimethyl-2-butanol (major product) CH3 C CH CH3 CH3 CH3 CH3 C CH CH3 CH3 CH3 CH3 C CH CH3 CH3 OH CH3 2 o , less stable 3 o , more stable Rearrangement:
Solved Problem 1 Show how you would accomplish the following synthetic conversions. (a)Convert 1-methylcyclohexene to 1-bromo-1-methylcyclohexane. Solution This synthesis requires the addition of HBr to an alkene with Markovnikov orientation.Ionic addition of HBr gives the correct product. CH; HBr Br 1-methylcyclohexene 1-bromo-1-methylcyclohexane Chapter 8 17
Chapter 8 17 Show how you would accomplish the following synthetic conversions. (a) Convert 1-methylcyclohexene to 1-bromo-1-methylcyclohexane. This synthesis requires the addition of HBr to an alkene with Markovnikov orientation. Ionic addition of HBr gives the correct product. Solved Problem 1 Solution
Solved Problem 2 Convert 1-methylcyclohexanol to 1-bromo-2-methylcyclohexane. Solution This synthesis requires the conversion of an alcohol to an alkyl bromide with the bromine atom at the neighboring carbon atom.This is the anti-Markovnikov product,which could be formed by the radical- catalyzed addition of HBr to 1-methylcyclohexene. CH R-0-0-R HBr heat Br 1-methylcyclohexene 1-bromo-2-methylcyclohexane 1-Methylcyclohexene is easily synthesized by the dehydration of 1-methylcyclohexanol.The most substituted alkene is the desired product. CH OH H2S04 H,0 heat 1-methylcyclohexanol I-methylcyclohexene Chapter 8 18
Chapter 8 18 Convert 1-methylcyclohexanol to 1-bromo-2-methylcyclohexane. This synthesis requires the conversion of an alcohol to an alkyl bromide with the bromine atom at the neighboring carbon atom. This is the anti-Markovnikov product, which could be formed by the radicalcatalyzed addition of HBr to 1-methylcyclohexene. 1-Methylcyclohexene is easily synthesized by the dehydration of 1-methylcyclohexanol. The most substituted alkene is the desired product. Solved Problem 2 Solution
Solved Problem 2(Continued) Solution (Continued) The two-step synthesis is summarized as follows: CH3 H2S04 HBr CH3 OH heat ROOR Br 1-methylcyclohexanol 1-methylcyclohexene 1-bromo-2-methylcyclohexane Chapter8 19
Chapter 8 19 The two-step synthesis is summarized as follows: Solved Problem 2 (Continued) Solution (Continued)
Oxymercuration-Demercuration Reaction Oxymercuration-Demercuration Hg(OAc)2 NaBHa HO HgOAc HO H (Markovnikov orientation) Copyright2010 Pearson Prentice Hall,Inc. Markovnikov addition of water to the double bond. ·No rearrangements. This is a two-step process. Chapter 8 20
Chapter 8 20 Oxymercuration–Demercuration Reaction • Markovnikov addition of water to the double bond. • No rearrangements. • This is a two-step process