Development and application of selective olefin synthesis utilizing the unique features of the silicon atom

(1)(t-BuO)Ph_2SiCH_2CN与脂肪醛和芳香醛的Peterson反应不仅在92：8~99：1范围内具有高的Z-选择性。(2)在(Pho)_2P(O)CH_2C(O)NRR‘与醛的Horner-Wadsworth-Emmons反应中，发现在某些情况下可以获得高的Z-选择性。与Peterson试剂Ph_3Si CH_2C(O)NHR相比，(Pho)_2P(O)CH_2C(O)NHR可用于烯化反应。(3)由(CF_3CH_2O)_2P(O)CH_2C(O)N(OMe)Me或(o-TolylO)_2P(O)CH_2C(O)N(OMe)Me制备的β-单取代-α，β-不饱和Weinreb酰胺，与有机稀土试剂反应，双键几乎不发生任何异构化，有效地生成相应的β-单取代-α，β-不饱和酮。对于β-单取代-α，β-不饱和Weinreb酰胺的制备，静止型试剂更适合于芳香醛，而Ando型试剂更适合于脂肪族试剂。(4)为了阐明导致(t-BuO)Ph_2SiCH_2CN反应高Z-选择性的因素，用模型化合物Rch(OSiR‘_3)CHMeCN进行了机理研究。反式化合物仅在碱处理时得到z-烯烃，而合成型化合物则导致混合物。前者的结果表明烯烃比主要由第一加成步骤决定，而后者则表明空间位阻在决定E1cb反应中有利于去质子化的构象中起主要作用。

(1)The Peterson reaction between (t-BuO)Ph_2SiCH_2CN and not only aliphatic aldehydes but also aromatic aldehydes proceeded with high Z-selectivity in the range of 92:8 to >99:1.(2)In the Horner-Wadsworth-Emmons reaction between (PhO)_2P(O)CH_2C(O)NRR' and aldehydes, it was found that high Z-selectivity could be achieved in some cases. Furthermore, it was found that amide reagent (PhO)_2P(O)CH_2C(O)NHR bearing a free hydrogen upon the nitrogen atom could be used for olefination in contrast to the Peterson reagent Ph_3Si CH_2C(O)NHR.(3)It was found that β-monosubstituted-α,β-unsaturated Weinreb amides, prepared from either (CF_3CH_2O)_2P(O)CH_2C(O)N(OMe)Me or (o-TolylO)_2P(O)CH_2C(O)N(OMe)Me, react with organocerium reagents with hardly any isomerization of the double bond to efficiently yield the corresponding β-monosubstituted-α,β-unsaturated ketone. For the preparation of β-monosubstituted-α,β-unsaturated Weinreb amides, the Still type reagent was more appropriate for aromatic aldehydes whereas the Ando type reagent was better for aliphatic reagents.(4)In order to elucidate the factors leading to high Z-selectivity in the reaction of (t-BuO)Ph_2SiCH_2CN, a mechanistic examination was carried out using model compounds RCH(OSiR'_3)CHMeCN. The anti compounds gave the z-olefins exclusively upon treatment with base whereas the syn compounds lead to mixtures. The former results imply that the olefin ratio is determined primarily by the first addition step, while the latter suggests that sterics plays a major role in determining the favored conformation for deprotonation in E1cb reactions.