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| PAPER | Synthesis 2004: 1814-1820
DOI: 10.1055/s-2004-829165 |
© Georg Thieme Verlag Stuttgart · New York
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Preparation of (E)-1-Alkenylboronic Acid Pinacol Esters via Transfer of Alkenyl Group from Boron to Boron
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| Kazuya Shirakawaa, Akira Araseb, Masayuki Hoshi*a |
a Department of Applied and Environmental Chemistry, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
Fax: +81(157)247719; e-Mail: hoshi-m@chem.kitami-it.ac.jp;
b 162-3 koen-cho, Kitami, Hokkaido 090-0015, Japan
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Received
22 March 2004 |
Abstract
Two synthetic routes to (E)-1-alkenylboronic acid pinacol esters 3 were investigated. Hydroboration of 1-alkynes 1 with 1,3,2-benzodioxaborole (catecholborane), in situ generated by the reaction of BH3 in THF with catechol, proceeded in the presence of a catalytic amount of dicyclohexylborane in THF at room temperature to give the corresponding (E)-1-alkenylboronic acid catechol esters 2. Treatment of the resultant esters 2 with 2,3-dimethyl-2,3-butanediol (pinacol) easily afforded the desired products 3, which are insensitive to air, moisture and chromatography, in good to high overall yields. The sequential reaction is a highly efficient route to 3 from BH3 in THF in a one-pot manner. Alternatively, hydroboration of 1 with 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (pinacolborane) was achieved in the presence of a catalytic amount of dicyclohexylborane at room temperature under neat conditions to afford the corresponding products 3 directly in good to excellent yields. This route is extremely efficient and environmentally benign from the viewpoints of making good use of pinacolborane and of using no solvent, and is capable of using a variety of alkynes 1 including functionalized ones such as HCCCH2Cl and HCCCH2OTHP. Key words
(E)-1-alkenylboronic acid pinacol ester - 1-alkyne - dicyclohexylborane - catecholborane - pinacolborane
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