Advices For Studying Organic Chemistry

1-Methylcyclopentene trans-2-Methylcyclopentanol (86%)

CH + enantiomer

3

H CH^3

OH

H 2 O 2 , OH−

H

1. THF: H 3


2. 
   

B

11.7A THE STEREOCHEMISTRY OF HYDROBORATION

1. The net result of hydroboration-oxidation is a syn addition of –H and –OH to a
   double bond.

Figure 11.1 The hydroboration-oxidation of 1-methylcyclopentene. The first
reaction is a syn addition of borane. (In this illustration we have
shown the boron and hydrogen both entering from the bottom side of
1-methylcyclopentene. The reaction also takes place from the top side
at an equal rate to produce the enantiomer.) In the second reaction
the boron atom is replaced by a hydroxyl group with retention of
configuration. The product is a trans compound (trans-2-methyl-
cyclopentanol), and the overall result is the syn addition of –H
and –OH.

11.7B PROTONOLYSIS OF ORGANOBORANES

1. Heating an organoborane with acetic acid causes cleavage of the C–B bond:
   
   
   1. This reaction also takes place with retention of configuration ⇒ the
      stereochemistry of the reaction is like that of the oxidation of organoboranes ⇒
      it can be very useful in introducing deuterium or tritium in a specific way.