Golden opportunities in stereoselective catalysis
Golden opportunities in stereoselective catalysis
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DOI：
10.1002/anie.200704729
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Krause, Norbert
中科院分区：
文献类型：
--
作者：
Bongers, Nadine;Krause, Norbert
The use of gold in homogeneous catalysis has witnessed tremendous activity in recent years.[1] This is mainly due to the unique ability of gold (I) and gold (III) salts to act as soft carbophilic Lewis acids towards carbon–carbon double and triple bonds which, after this activation, undergo a variety of transformations that lead to new carbon–carbon or carbon–heteroatom bonds. Despite its utility, however, applications of homogeneous gold catalysis in stereoselective organic synthesis are still rare. This is all the more surprising since one of the first examples of the use of homogeneous gold catalysis in organic synthesis was actually a highly enantioselective reaction: In 1986, Ito et al.[2] had already published a seminal paper in which [Au (c-HexNC) 2]+ BF4 À together with the chiral ferrocenylphosphane ligand A was used as a catalyst for the enantioselective aldol reaction of aldehydes with isocyanates to yield 5-alkyl-2-oxazoline-4-carboxylates with enantioselectivities of up to 97% ee and trans/cis ratios ranging from 80: 20 to 100: 0 (Scheme 1). These products are valuable precursors for b-hydroxyamino acids and related compounds.[3]Surprisingly, this potentially ground-breaking contribution was mostly ignored in later years. Only at the beginning of this century was the potential of homogenous gold catalysis in stereoselective organic synthesis again recognized. The transformations developed since rely either on the transfer of chirality from a substrate with a defined configuration to the product, or on the introduction of chirality into a prochiral substrate through the use of chiral gold catalysts. The transfer of stereochemical information from a substrate to a product by gold-catalyzed rearrangement or cyclization has turned out to be a highly successful strategy. The reactivity and inherent axial chirality of allenes make them particularly attractive starting materials for this purpose. For example, the gold (I)-or gold (III)-catalyzed endocycloisomerization of a-and b-hydroxyallenes to the corresponding five-and six-membered heterocycles occurs with complete transfer of chirality in most cases (Scheme 2).[4] The
