1559T_ch12_220-24611/02/0521:55Pa9e222 EQA 222.Chapter 12 REACTIONS OF ALKENES useful because the new carbon-boron bond can be oxidized by basic HO to give an alcohol. --一-C-0m The chart that follows summarizes the new reactions of Sections 12-3 through 12-8,using 1-methylcyclo- 1.Hydroboration-oxidation(anti-Markovnikov).e.g.. -aH=at0a--a-at CH3 OH CH-C-CH-CH2-OH H02 2.Oxymercuration-demercuration (Markovnikov).e.g. CH3 CH3OH CH-C-CH-CH.CH-c-CH-CH CH3 HgOAc CHsOH :-CH-CHs 3.Acid-catalyzed hydration (Markovnikov,with carbocations that may rearrange).e.g.. CHs CHs CH;- -C-CH-CH2 H, H.O CH,- -CH-CH H CH CH;-C-CH-CHs CH;- CH-CH CH. Borane BOH bonds add across alkenes. The reaction (1) is regioselectively anti-Markovnikov, (2) is stereospecifically a syn addition, (3) goes by a concerted, one-step mechanism, and (4) is synthetically very useful because the new carbon–boron bond can be oxidized by basic H2O2 to give an alcohol. The chart that follows summarizes the new reactions of Sections 12-3 through 12-8, using 1-methylcyclo￾hexene as a substrate. Note the three methods for adding H2O to a double bond, each with its own specific characteristics. 1. Hydroboration–oxidation (anti-Markovnikov), e.g., 2. Oxymercuration–demercuration (Markovnikov), e.g., 3. Acid-catalyzed hydration (Markovnikov, with carbocations that may rearrange), e.g., C CH3 CH3 CH2 CH3 CH H2SO2 H2O C CH CH3 CH3 CH3 CH3  C CH CH3 CH3 CH3 CH3  C CH CH3 CH3 OH CH3 CH3 C CH3 CH3 CH2 CH3 CH Hg(OAc)2 H2O THF NaBH4 NaOH H2O C CH CH3 CH3 CH3 OH HgOAc CH2 OH C CH CH3 CH3 CH3 CH3 C CH3 CH3 CH2 CH3 CH 3 ( ( BH3 THF C CH2 CH3 CH3 CH3 CH2 B NaOH H2O2 C CH2 OH CH3 CH3 CH3 CH2 C B C OH 222 • Chapter 12 REACTIONS OF ALKENES 1559T_ch12_220-246 11/02/05 21:55 Page 222