| Abstract
| - The reaction of sterically hindered boronic esters with thionyl chloride and heterocyclic amines to form alkylboron chloride amine complexes is catalyzed by borosilicate glass.
- Sterically hindered boronic esters of (R,R)-1,2-dicyclohexyl-1,2-ethanediol or pinanediol react withthionyl chloride and excess imidazole in acetonitrile ona borosilicate glass surface (but not on silica or soda-lime glass) to form the corresponding cyclic sulfite of thediol and the easily separable organoborane derivativecontaining one boron-bound chloride and two imidazolegroups, which may cross link with additional organoborane moieties to form oligomeric species. Other heterocyclic amines react similarly but usually less efficiently.With excess pyridine, the 1:1 complex PhBCl2(py) rapidlyforms the 2:1 complex, PhBCl(py)2+Cl-. Hydrolysis of theamino boron chlorides to boronic acids in near neutralaqueous solution provides a mild process for the nethydrolysis of hindered boronic esters, many of whichcannot be hydrolyzed by ordinary means, though yieldswere only 54−82%. The diol sulfites are stable towardwater or aqueous acid but rapidly hydrolyzed by baseto the diol and inorganic sulfite.
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