Kurono Nobuhito, Kondo Tadahiro, Wakabayashi Masanori, Ooka Hirohito, Inoue Tsutomu, Tachikawa Hiroto, Ohkuma Takeshi
Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University, Sapporo, Japan.
Chem Asian J. 2008 Sep 1;3(8-9):1289-97. doi: 10.1002/asia.200700420.
Enantiomer-selective carbamoylation of racemic alpha-hydroxy gamma-lactones with half equivalents of isocyanates in the presence of chiral Cu(II) catalysts was studied. Among a series of catalyst bearing chiral bis(oxazoline) (box) and pyridine(bisoxazoline) ligands, [Cu(tBu-box)]X(2) [X=OSO(2)CF(3) (3 a), SbF(6) (3 b)] showed the highest enantioselectivity in the reaction of pantolactone (1 a). Use of n-C(3)H(7)NCO, a small alkyl isocyanate, in CH(2)Cl(2) solution was important to achieve a high level of enantiomer selection. The tBu-box-Cu(II) catalyst efficiently differentiated two enantiomers of beta-substituted alpha-hydroxy gamma-lactones under the optimized reaction conditions, resulting in a stereoselectivity factor (s=k(fast)/k(slow)) of up to 209. Furthermore, this catalyst is highly active, so that the carbamoylation can be conducted with a substrate-to-catalyst molar ratio of 2000-3000. A catalytic cycle of this reaction is also proposed.
研究了在手性铜（II）催化剂存在下，用半当量异氰酸酯对消旋α-羟基γ-内酯进行对映体选择性氨甲酰化反应。在一系列带有手性双（恶唑啉）（box）和吡啶（双恶唑啉）配体的催化剂中，[Cu(tBu-box)]X(2) [X = OSO(2)CF(3) (3 a)，SbF(6) (3 b)]在泛内酯（1 a）的反应中表现出最高的对映选择性。在二氯甲烷溶液中使用小烷基异氰酸酯正丙基异氰酸酯对于实现高水平的对映体选择性很重要。在优化的反应条件下，tBu-box-Cu(II)催化剂能有效区分β-取代的α-羟基γ-内酯的两种对映体，立体选择性因子（s = k(fast)/k(slow)）高达209。此外，该催化剂活性很高，因此氨甲酰化反应可以在底物与催化剂的摩尔比为2000 - 3000的条件下进行。还提出了该反应的催化循环。
