Kazuya Shirakawa, A. Arase, M. Hoshi
Jul 22, 2004
Citations
0
Influential Citations
21
Citations
Journal
Synthesis
Abstract
Two synthetic routes to (E)-1-alkenylboronic acid pinacol esters 3 were investigated. Hydroboration of 1-alkynes I with 1,3,2-benzodioxaborole (catecholborane), in situ generated by the reaction of BH 3 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 BH 3 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 HCCCH 2 Cl and HCCCH 2 OTHP.