Biomimetic carbene catalyzed oxidative activation of aldehydes

卡宾已被广泛用作缩醛的催化剂。研究充分的安息香缩合反应和Strecker反应就是突出的例子。在这些过程中，卡宾催化剂被用来中间生成所谓的布雷斯洛中间体，该中间体进一步在离子过程中与醛、活化的贫电子双键或与其他亲电体反应。最近，在布雷斯洛中间体的-位置上的离开基团已经被安装以将烯醇醚转移到活化的酰基卡宾离子中。大多数卡宾催化的醛转化反应涉及布雷斯洛中间体的离子转化。在该方案中，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卡宾离子。这种自然使用的卡宾催化剂到目前为止在合成上还没有得到很好的研究。在氧气中，将测试其他对环境无害的单电子转移氧化剂，特别是氮氧化物。在这些有机催化反应中，将避免使用金属基氧化剂。，-不饱和醛的活化会产生活化的迈克尔受体，需要进行1，4-加成反应。我们计划通过卡宾催化的氧化还原活化来研究醇、保护胺和硫醇的分子内1，4-立体选择性加成反应。此外，酰基卡宾离子还将用于分子内过渡金属自由醛的C-H活化反应，以生成环酮。

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.