Organotrifluoroborate salts.pdf

/Elements/005/index.html Frontiers in Chemistry: May 17, 2008 David Arnold Organotrifluoroborate Salts: Versatile Reagents in Organic Synthesis David Arnold @ Wipf Group Page 1 of 35 5/18/2008 Exponential Growth in the Number of Publications Dedicated to Potassium Organotrifluoroborates Over the Last 10 Years Chem. Rev. 2008, 108, 288 R B F F F K+ - R = alkyl, alkenyl, alkynyl, allyl, crotonyl, aryl David Arnold @ Wipf Group Page 2 of 35 5/18/2008 Outline ? A Brief History on the Preparation of Organotrifluoroborate Salts ? General Preparation of Organotrifluoroborate Salts ? Functionalization of Potassium Organotrifluoroborates ? Selected Reactions of Potassium Organotrifluoroborates ? Applications to Natural Product Synthesis ? Conclusions David Arnold @ Wipf Group Page 3 of 35 5/18/2008 A Brief History on the Preparation of Organotrifluoroborate Salts ? Laboratory curiosities in the 1960: Preparation of the first organotrifluoroborate salt and the first stable compound containing a trifluoromethyl-boron linkage: Me3Sn SnMe3 + CF3I h! Me3SnCF3 BF3 gas CCl4 Me3Sn(CF3BF3) KF H2O CF3BF3K J. Am. Chem. Soc. 1960, 82, 5298. ? Preparation from dihaloorganoboranes: J. Organomet. Chem. 1988, 340, 267. ? A breakthrough in the preparation of organotrifluoroborate salts lies dormant: Thierig and Umland 1967 B N H2 O Ph Ph KHF2 AcOH, ! PhBF3K Naturwissenschaften 1967, 54, 563. BBr2 KF (3 eq.) H2O, 89% BF3K David Arnold @ Wipf Group Page 4 of 35 5/18/2008 Revisiting the Past, Vedejs 1995: The Revolution Begins PhB(OH)2 Excess KHF2 (aq) MeOH, rt, 15 min 82% PhBF3K Me3SiCl THF PhBF2 in situ ? Convenient preparation of aryltrifluoroborate salts from boronic acids and in situ conversion to arylboron difluoride Lewis acids BF3K BF3K BF3K BF3K O BF3KF F3C CF3 Cl Cl F 94% 68% 53% 76% 48% ? All salts were found to be air and moisture stable crystalline solids which could be synthesized on a multigram scale and purified by simple recrystallization from ace