2,3-Butanediol boronic esters

Boronic esters having oxygenated substituents, for example, R2 = C(OCH3)(CH3)2, yield poor diastereoselection24 2,3-Butanediol esters (R2 = CH3) yield approximately 20 1 diastere-omeric ratios25 -27. 

The addition of excess methanol to l-chloro-/ra t-2,5-diphenylborolane 27 yielded the boronic ester 28 in 57% yield together with boronic and borate esters in 30% and 12% yield, respectively. On the other hand, oxidation of 1-chloroborolane 27 with 3 equiv of sodium perborate gave the water-soluble l,4-diphenyl-/ra r-l,4-butanediol 59 in 55% yield (Scheme 5) <1997TL8487>. 

Boronic ester homologation. (R,R)-2,3-Butanediol- and (-(- )-pinanediol have been used as the chiral adjuncts in a diastereoselective homologation of dichloromethaneboronic esters (1) to the (aS)-a-chloroboronic esters (2). Reaction of 1 with an alkyllithium produces a borate complex (a), which rearranges diastereoselectively in the presence of ZnCl, to 2 with introduction of a chiral center adjacent to boron. The reaction permits... 

S,S)-Diisopropylethanediol and (/ ,/ )-2,3-butanediol are also effective chiral directors in boronic ester rearrangements. Both of these vicinal diols are C symmetric and the butanediolboronic esters are readily hydrolyzed to boronic acids, which can then be reesterified if a change in chiral direction is required. 

This auxiliary-controlled synthesis was later studied by others [37, 38] and 2R,3R)-l,4-dimethoxy-l,l,4,4-tetraphenyl-2,3-butanediol was proven to be both an efficient chiral director and protecting group in the cyclopropanation of boronic esters [39-42]. These compounds are stable on silica gel, which allows the chromatographic separation of the diastereoisomers. The influence of an additional stereogenic center in the side chain of the alkene has also been examined [43], as well as substrate-... 

B NMR spectroscopy has been used to study ester and complex formation in the system HsBOs-NaOH H20-2,3-butanediol. Heteronuclear complexes of zinc and boron with hydroxyethylidenediphosphonic acid have been investigated by B and P NMR spectroscopy. The interaction between D-glucose and sodium monoborate has been studied using B and C NMR spectroscopy. ... 

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