Development of New Synthetic Reactions Using Organosilicon Compounds

大多数有机硅试剂都有一个三甲基硅基（TMS）或一个更大的三有机硅基。硅基体积较小的硅试剂的合成用途尚未得到探索。我们发现二甲基硅基（DMS）保护的亲核试剂比tms保护的亲核试剂更具活性。例如，在CaCl_2存在下，酮类DMS烯醇化物在DMF中30℃下与醛类化合物顺利加成，得到产率较高的醛类化合物。在相同条件下，相应的TMS烯化物完全不与醛发生反应。在DMS烯醇酸反应中，氯化钙作为路易斯碱通过氯离子对硅的亲核攻击激活烯醇酸。DMS烯醇化物可用于n -苯胺的mannich型反应和a-烯酮的Michael反应。同样，α- dms酯比相应的tms基试剂反应性更强。在金属氯化物（LiCl， MgCl_2等）存在下，醛类和酮类发生了α- dms酯的高效醛醇反应。一般来说，氢硅烷不与碳亲电试剂自发反应；然而，它们的还原能力可以通过激活底物或自身来获得。正确选择活化剂可以对还原过程进行精细控制。我们发现PhSiH_3在in （OAc_3）存在下与卤代烷烃反应生成脱卤代烷烃。这种还原涉及到一个由氢化铟物种介导的自由基链。PhSiH_3-In（OAc_3）体系适用于卤代烷烃与缺电子烯烃的分子间自由基加成。此外，对α -烯酮与醛的还原性醛醇反应也有一定的研究价值。在这种情况下，一个合理的机制包括离子1,4-还原与氢化铟和醛醇反应所产生的铟烯醇化物。

Most of organosilicon reagents have a trimethylsilyl (TMS) group or a more bulky triorganosilyl group. Synthetic utility of silicon reagents bearing a less bulky silyl group has remained unexplored. We have found that dimethylsilyl (DMS)-protected nucleophiles are more reactive than TMS-protected nucleophiles. For example, in the presence of CaCl_2, ketone DMS enolates added smoothly to aldehydes at 30℃ in DMF to give aldols in high yield. Under the same conditions, the corresponding TMS enolates did not react with aldehydes at all. In the reaction of DMS enolates, CaCl_2 would serve as Lewis base to activate the enolates by nucleophilic attack of the silicon by the chloride ion. DMS enolates are useful for the Mannich-type reaction of N-tosylimines and the Michael reaction of a-enones. Similarly, α-DMS-esters are more reactive than the corresponding TMS-based reagents. In the presence of metal chlorides (LiCl, MgCl_2, etc.), aldehydes and ketones underwent efficient aldol reactions of α-DMS-esters.In general, hydrosilanes do not react spontaneously with carbon electrophiles ; however, their reducing ability can be drawn by activation of the substrates or themselves. A proper choice of activator enables fine control of the reduction process. We have found that PhSiH_3 reacts with haloalkanes in the presence of In(OAc_3) to form the dehalogenated alkanes. This reduction would involve a radical chain mediated by indium hydride species. The PhSiH_3-In(OAc_3) system is applicable to intermolecular radical addition of haloalkanes to electron-deficient alkenes. Additionally, it is valuable also for reductive aldol reaction of a-enones with aldehydes. In this case, a plausible mechanism consists of ionic 1,4-reduction of a-enones with indium hydride species and aldol reaction of the resultant indium enolates.