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反应在92:8 ~ 99:1范围内具有较高的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较高的z选择性。此外，与Peterson试剂Ph_3Si CH_2C(O)NHR相比，酰胺试剂（PhO）_2P(O)CH_2C(O)NHR在氮原子上携带一个游离氢可以用于烯烃。(3)发现由（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酰胺与有机铈试剂反应时，双键几乎没有异构化，可以有效地生成相应的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，Still型试剂更适合芳香醛类，而Ando型试剂更适合脂肪类试剂。(4)为了阐明导致（t-BuO）Ph_2SiCH_2CN反应具有高z选择性的因素，采用模型化合物RCH(OSiR’_3)CHMeCN进行了机理研究。抗化合物只在碱处理后得到z-烯烃，而合成化合物则得到混合物。前者的结果表明，烯烃比例主要由第一步加成决定，而后者表明，立体构型在决定E1cb反应中去质子化的有利构象方面起主要作用。

(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.