D A. Evans Olefin Oxymercuration-1 Chem 206 Oxymercuration Pasto JACS 1970, 92, 7480 Bromination of Cyclohexene Derivatives Pasto, JACS 1970, 92, 7480 The basic process Diaxial opening of bromonium ions may be viewed as an extension of the =”- NaBH Furst-Plattner Rule for epoxide ring opening.(Lecture-2) Case a Kinetics: Halpem, JACS 1967, 89, 6427 Reduction: Pasto, JACS 199, 91, 719 Overview B rown JoC 1981. 46. 3810 Me3C、 Oxy-Mercuration bromination follow identical pathways( Pasto) Br Me3C Meoh Me3C、 THF, H2O 53% OMe R=H41%48% OMe R=Me100% Meo Me3C、 Me exclusive product THF, H2O 8+ 仓Hgx Br Reduction of the Hg-C bond NaBH R-Hg-X R-Hg-H R-H observed HOMe OMe syn-Unreactive R-Hg From Case A. one assumes that both bromonium ions are formed: however Formate is an excellent source of hydride ion for for the syn isomer to react, ring opeing must proceed against the polarization late transition and heavy main-group metals due to Methyl substituentR Hg–X NaBH4 H Me3C Hg–X Me H H–CO2 – R Hg O H O –CO2 R Hg–H H Me3C Me H Me3C R THF, H2O R H Hg(OAc)2 H Me3C Hg–X Me H THF, H2O Hg(OAc)2 C C R H H H H Me3C OH HgOAc Me H H Me3C OH HgOAc R H ROH X–Hg–X H Me3C Br Me H C C R H H XHg H OR HOMe H Me3C HgOAc OH R H NaBH4 H Me3C Br Me H –H+ C C R H H H H OR H Me3C Me H Me3C Br Me H OMe H Me3C H MeOH MeOH H Me3C Br Me H MeOH H Me3C Br H H H Me3C OMe Br Me H H Me3C Br H H H Me3C Br OMe H H H Me3C OMe Br H H D. A. Evans Olefin Oxymercuration-1 Chem 206 R = H 41% 48% R = Me 100% Oxy-Mercuration & bromination follow identical pathways (Pasto) Oxymercuration Pasto, JACS 1970, 92, 7480 exclusive product syn-Unreactive anti-Reactive Reduction of the Hg–C bond nonstereoselective radical chain process Formate is an excellent source of hydride ion for late transition and heavy main-group metals The basic process: Kinetics: Halpern, JACS 1967, 89, 6427 Reduction: Pasto, JACS 199, 91, 719 Overview: B rown, JOC 1981, 46, 3810. d+ d+ Bromination of Cyclohexene Derivatives Pasto, JACS 1970, 92, 7480 Pyr–Br+ Br3 – 47% 53% Diaxial opening of bromonium ions may be viewed as an extension of the Furst-Plattner Rule for epoxide ring opening. (Lecture-2) Pyr–Br+ Br3 – exclusive product syn-Unreactive Case A Case B From Case A, one assumes that both bromonium ions are formed; however, for the syn isomer to react, ring opeing must proceed against the polarization due to Methyl substituent. anti-Reactive syn-Unreactive not observed d+ d+ d+