Integration of Catalysis and Analysis is the Key: Rapid and Precise Investigation of the Catalytic Asymmetric Gosteli–Claisen Rearrangement
作者:Johannes Troendlin、Julia Rehbein、Martin Hiersemann、Oliver Trapp
DOI:10.1021/ja207091x
日期:2011.10.19
The kinetics of the Cu-II(bisoxazoline)-catalyzed diastereoand enantioselective Gosteli-Claisen rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ethers has been investigated by enantioselective on-column reaction gas chromatography (ocRGC). Enantioselective ocRGC integrates (stereoselective) catalysis and enantioselective chromatography in a single microcapillary, which is installed in a GC-MS for direct analysis of conversion and selectivity. Thus, this technique allows direct differentiation of thermal and stereoselectively catalyzed reaction pathways and determination of activation parameters and selectivities of the individual reaction pathways starting from stereoisomeric reactants with high precision. Two modes of operation of enantioselective ocRGC are presented to investigate noncatalyzed, i.e., conversion of isopropyl-2-(allyloxy)but-2Z-enoate 1 to isopropyl-3R,S-methyl-2-oxy-hex-5-enoate (+/-)-2 and the [Cu(R,R)-Ph-box}](SbF6)(2)-catalyzed Gosteli-Claisen rearrangement, i.e., conversion of isopropyl-2-(but-2'E-en-1-yloxy)but-2Z-enoate (E,Z)-3 to isopropyl-3S,4S-dimethyl-2-oxy-hex-5-enoate 4b. Eyring activation parameters have been determined by temperature-dependent measurements: Uncatalyzed rearrangement of 1 to (+/-)-2 gives Delta G double dagger (298 K) = 114.1 +/- 0.2 kJ . mol(-1), Delta H double dagger = 101.1 +/- 1.9 kJ . mol(-1), and Delta S double dagger = -44 +/- 5 J . (K . mol)(-1), and catalyzed rearrangement of (E,Z)-3 to 4b gives Delta G double dagger (298 K) = 101.1 +/- 0.3 kJ . mol(-1), Delta H double dagger = 106.1 +/- 6.6 kJ . mol(-1), and Delta S double dagger = 17 +/- 19 J . (K . mol)(-1).