Synthesis of Chiral Tetrasubstituted Alkenes by an Asymmetric Cascade Reaction Catalyzed Cooperatively by Cationic Rhodium(I) and Silver(I) Complexes
Synthesis of Chiral Tetrasubstituted Alkenes by an Asymmetric Cascade Reaction Catalyzed Cooperatively by Cationic Rhodium(I) and Silver(I) Complexes
复制标题
DOI：
10.1002/anie.200904024
复制
发表时间：
2009-01-01
影响因子：
16.6
通讯作者：
Tanaka, Ken
中科院分区：
文献类型：
--
作者：
Hojo, Daiki;Noguchi, Keiichi;Tanaka, Ken
可以一步提供复杂有机分子的级联反应在有机合成中引起了广泛的关注。[1]显然，可以控制产物手性的不对称级联反应更具吸引力。[2]在这里，我们描述了一种新的不对称级联反应，它是由阳离子Rh(I)和Ag(I)配合物协同催化的。该反应可以产生具有螺旋和/或中心手性的四取代烯烃。[3]Feringa和他的同事已经证明，同时具有中心和螺旋手性的四取代螺旋烯烃可以应用于光驱动的分子马达。因此，螺旋烯烃正引起越来越大的兴趣。此外，目前的不对称级联反应可能包括阳离子过渡金属络合物对π-和σ键的前所未有的顺序激活。我们的研究小组最近报道了阳离子Rh(I)/手性双膦络合物催化2-炔基苯甲醛1与羰基化合物2进行高对映选择性的[4+2]环化反应，该反应高产率且具有高ee值(方案1)。[5][4+2]环化反应的机理被提出如下：[5，6]1的甲酰基的C±H键被激活而生成氢化铑物种，它在侧基上加成分子内的5元酰基罗丹环A。A与2，4，2的羰基之间的分子间[4+2]环加成另一方面，当在阳离子Rh(I)/(R，R)-SL-W001-1((R，R)-5)催化剂存在下进行2-炔基苯甲醛1a和N-甲基异氰酸酯(2a)的反应时，得到了意想不到的具有四取代烯基的苯并吡喃酮4AA和预期的苯并吡喃酮3AA(方案2)。手性配体的筛选表明，使用(R，R)-SL-W005-1((R，R)-6)以几乎定量的产率提供了4个氨基酸，并且具有高的ee值(方案2)。然而，在阳离子Rh(I)催化剂存在下，2-炔基苯甲醛1(在炔端具有烷基、异丙烯或芳基)和2a与(R，R)-5或(R，R)-6提供的苯并吡喃酮3高产率地反应，并且只产生微量的苯并吡喃酮4(<；2%产率)。四取代烯烃4-AA的形成机理如图式3所示。有很多
Cascade reactions that can furnish complex organic molecules in one step have attracted much attention in organic synthesis.[1] Obviously, asymmetric cascade reactions that can control the chirality of the product are more attractive.[2] Herein, we describe a novel asymmetric cascade reaction that is catalyzed cooperatively by cationic rhodium (I) and silver (I) complexes. The reaction can produce tetrasubstituted alkenes which possess helical and/or central chirality.[3] Feringa and co-workers have demonstrated that tetrasubstituted helical alkenes, which possess both central and helical chirality, can be applied to light-driven molecular motors.[4] Therefore helical alkenes are attracting growing interest. Furthermore, the present asymmetric cascade reaction might include unprecedented sequential activation of π-and σbonds by cationic transition-metal complexes. Our research group has recently reported that a cationic rhodium (I)/chiral bisphosphine complex catalyzes a highly enantioselective [4+ 2] annulation of 2-alkynylbenzaldehydes 1 with carbonyl compounds 2, and the reaction leads to benzopyranones 3 in high yields and with high ee values (Scheme 1).[5] The mechanism of the [4+ 2] annulation is proposed as follows:[5, 6] A rhodium hydride species is generated through activation of the CÀH bond of the formyl group of 1, which adds intramoleculary to the pendant alkyne to give five-membered acylrhodacycle A. An intermolecular [4+ 2] cycloaddition between A and the carbonyl group of 2, and subsequent reductive elimination furnishes optically active benzopyranone 3. On the other hand, when the reaction of 2-alkynylbenzaldehyde 1a, possessing a cyclohexenyl group at the alkyne terminus, and N-methylisatin (2a) was conducted in the presence of a cationic rhodium (I)/(R, R)-SL-W001-1 ((R, R)-5) catalyst, the unexpected benzopyranone 4 aa, possessing a tetrasubstituted alkene moiety, was obtained along with the expected benzopyranone 3 aa (Scheme 2). Screening of chiral ligands revealed that the use of (R, R)-SL-W005-1 ((R, R)-6) furnished 4 aa in almost quantitative yield with a high ee value (Scheme2). However the reactions of 2-alkynylbenzaldehydes 1, possessing an alkyl, isopropenyl, or aryl group at the alkyne terminus, and 2a in the presence of the cationic rhodium (I) catalyst with (R, R)-5 or (R, R)-6 furnished benzopyranones 3 in high yields, and only trace amounts (< 2% yield) of benzopyranones 4 were generated. A possible mechanism for the formation of tetrasubstituted alkene 4 aa is shown in Scheme3. There are many