B6 Boronic ester homologation

Reaction of boronic esters, RB(OR )2, with dichloromethyllithium, LiCHCl2, inserts the CHC1 unit into the carbon-boron bond of the boronic ester. This is known as boronic ester homologation. If boronic esters derived from homochiral alcohols are used in this reaction, then new homochiral centres may be generated as will be illustrated below. 

Expensive OSO4 may be used in catalytic amounts to oxidize alkenes to diols if MesNO is added. This reagent efficiently reoxidizes the osmium back to 0s04 during the course of the reaction. 

Many boronic ester homologation reactions have been performed using pinanediols as chiral auxiliaries. These are readily available from (+)- and (-)-a-pinene by osmium tetroxide-catalyzed oxidation reactions (Equations B6.1 and B6.2). 

Addition of a wide range of boronic acids [RB(OH)2] or esters [RB(OR )2] to the pinanediols gives the very stable pinanediol boronic esters. For example, propylboronic acid (available from the addition of propylmagnesium bromide to trimethyl borate followed by acid hydrolysis) and the (s) pinanediol combine to give a homochiral boronic ester as shown in Equation B6.3. 

CHCI2 group. Empirically the addition and rearrangement steps generate an S 

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