Biomimetic carbene catalyzed oxidative activation of aldehydes

羰基已被广泛用作醛类化合物合成的催化剂。研究得比较充分的安息香缩合反应和斯特莱克反应就是突出的例子。在这些过程中，碳催化剂用于中间生成所谓的布雷斯洛中间体，该中间体进一步以离子过程与醛、与激活的电子贫双键或与其他亲电试剂反应。最近，在Breslow中间体的-位置上安装了离去基团，以将烯醇醚转移到活化的酰基碳离子中。大多数碳催化的醛的转化都是由布雷斯洛中间体的离子转化引起的。在这个建议中，我们使用单电子转移氧化试剂在仿生过程中形成活化的酰基碳离子。这种性质的催化作用也为自然界所使用，但迄今为止在合成中还没有得到很好的研究。在双氧中，其他环境友好的单电子转移氧化剂，特别是氮氧化物将被测试。在这些有机催化反应中应避免使用金属基氧化剂。，-不饱和醛的活化将产生活化的迈克尔受体，该受体应进行1,4加成反应。我们计划通过碳催化氧化还原活化研究分子内立体选择性1,4醇、保护胺和硫醇的加成。此外，酰基正碳离子也将用于分子内过渡金属游离醛c - h活化反应，以形成环酮。

Carbenes have been intensively used as catalysts for the umpolung of aldehydes. The well investigated benzoin condensation and the Strecker reaction are prominent examples. In these processes the carbene catalyst is used to intermediately generate the so called Breslow intermediate which further reacts in an ionic process with an aldehyde, with an activated electron-poor double bond or with other electrophiles. More recently, leaving groups at the -position of the Breslow intermediate have been installed to transfer the enol ether into an activated acylcarbenium ion. Most of the carbene-catalyzed transformations of aldehydes deal with ionic transformations of the Breslow intermediate. In the proposal we use single electron transfer oxidation reagents for the formation of activated acylcarbenium ions in biomimetic processes. This type of carbene catalysis also used by nature is not well investigated so far in synthesis. Among dioxygen other environmentally benign single electron transfer oxidants in particular nitroxides will be tested. Metal based oxidants will be avoided in these organocatalyzed reactions. Activation of ,-unsaturated aldehydes will generate activated Michael acceptors which should undergo 1,4-addition reactions. We plan to study stereoselective intramolecular 1,4-additions of alcohols, protected amines and thiols via carbene catalyzed redox activations. Moreover, acylcarbenium ions will also be used in intramolecular transition metal free aldehyde C-H-activation reactions for the formation of cyclic ketones.