Synthesis of ethers
Mixed acetals and organotrifluoroborates undergo BF3·OEt2-promoted cross-couplings to give dialkyl ethers under simple, mild conditions. A survey of reaction partners identified a hydroxamate leaving group that improves the regioselectivity and product yield in the BF3·OEt2-promoted coupling reaction of mixed acetals and potassium alkynyl-, alkenyl-, aryl- and heteroaryltrifluoroborates.
C.-V. T. Vo, T. A. Mitchell, J. W. Bode, J. Am. Chem. Soc., 2011, 133, 14082-14089.
InOTf is as an effective Lewis acid catalyst for unprecedented nucleophilic substitution of acetals with allylboronates. A transmetalative SN1 mechanism is proposed in which a single InI center acts as a dual catalyst to activate both reagents sequentially. Contrary to the classic γ-selectivity of allylsilanes (Hosomi-Sakurai reaction), this InI-catalyzed borono variant displays distinct α-selectivity.
U. Schneider, H. T. Dao, S. Kobayashi, Org. Lett., 2010, 12, 2488-2491.
Ga(I)-catalyzed C-C bond formations between allyl or allenyl boronic esters and acetals, ketals, or aminals have proceeded in high yields with essentially complete regio- and chemoselectivity by using a catalytic amount of Ga(0), a Ag(I) cocatalyst, crownether ligation, and ultrasonic activation.
B. Qin, U. Schneider, J. Am. Chem. Soc., 2016, 138, 13119-13122.