Synthesis of “Garner” Aldehyde‐Derived Cyclopropylboronic Esters

The “Garner” aldehyde has been used as a common intermediate for the preparation of the corresponding alkyne 7 and the alkenylboronic esters 12−16 (24−80%). Diastereoselective cyclopropanation afforded cyclopropylboronic esters 17−20 (60−84%, dr 22:78 to 92:8), the configurations of which were determined by chemical correlation (cyclopropanols 22), X‐ray structural analysis (of 21a), and characteristic NMR spectroscopic data. The protected amino alcohols 23−26 and amino acids 27 have been synthesised from the cyclopropylboronic esters 19 by oxidation, Matteson homologation or Suzuki coupling. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)