(2R,3R)-1,4-Dimethoxy-1,1,4,4-tetraphenyl-2,3-butanediol:  Chiral Auxiliary and Efficient Protecting Group for Boronic Acids

(2R,3R)-1,4-Dimethoxy-1,1,4,4-tetraphenyl-2,3-butanediol (1) has been used as an efficient chiral auxiliary in the cyclopropanation of alkenylboronic esters. The stability of the obtained cyclopropylboronic esters allowed the chromatographic separation of the diastereoisomers. Furthermore, it enabled a variety of transformations in the side-chain, including oxidation, reduction, and reactions under acidic, basic, or radical conditions, that finally led to boron containing functionalized bicyclopropanes, e.g., 12 and 18. The absolute configurations of these building blocks were established by X-ray crystallography (compound 10) and by chemical correlation. The Matteson homologation led to a known advanced intermediate of the oligocyclopropane FR-900848.