Oisaki Kounosuke, Zhao Dongbo, Kanai Motomu, Shibasaki Masakatsu
Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0013, Japan.
J Am Chem Soc. 2007 Jun 13;129(23):7439-43. doi: 10.1021/ja071512h. Epub 2007 May 16.
A general catalytic asymmetric alkylative aldol reaction is described as a new entry to the catalytic asymmetric multicomponent reaction (CAMCR). Highly functionalized delta-lactones were produced in the presence of a catalytic amount of the Cu(OAc)2-DIFLUORPHOS complex through three-component assembly of dialkylzincs, allenic esters, and unactivated ketones. This CAMCR constructs two C-C bonds and one tetrasubstituted chiral center simultaneously. Conjugate addition of alkylcopper species to an allenic ester produced highly active copper enolate in situ, and the successive asymmetric aldol addition to ketones followed by lactonization afforded the desired products. The addition of MS4A and Lewis base (Ph2S=O, DMSO, or HMPA) is important for obtaining a high yield, with suppression of the undesired alpha-addition pathway. Control/crossover experiments suggest that the addition of a Lewis base facilitated the retro-aldol reaction of the alpha-adducts (proofreading effect). The ketone and copper enolate generated through the retro-aldol reaction were converted to the desired lactone through the gamma-aldol pathway, which was trapped by irreversible lactone formation.
一种通用的催化不对称烷基化羟醛反应被描述为催化不对称多组分反应(CAMCR)的一种新方法。在催化量的Cu(OAc)₂ - DIFLUORPHOS配合物存在下,通过二烷基锌、丙二烯酸酯和未活化酮的三组分组装生成了高度官能化的δ-内酯。这种CAMCR同时构建了两个C-C键和一个四取代手性中心。烷基铜物种向丙二烯酸酯的共轭加成原位生成了高活性的铜烯醇盐,随后向酮的连续不对称羟醛加成然后内酯化得到了所需产物。添加MS4A和路易斯碱(Ph₂S=O、DMSO或HMPA)对于获得高产率很重要,同时抑制了不期望的α-加成途径。对照/交叉实验表明,路易斯碱的添加促进了α-加合物的逆羟醛反应(校对效应)。通过逆羟醛反应生成的酮和铜烯醇盐通过γ-羟醛途径转化为所需的内酯,该途径被不可逆的内酯形成所捕获。