Stereoselective Synthesis Using iVee-Membered Carbon Ring and Silyl Groups

酰基硅烷与亚甲基硫化物反应，甜菜碱中间体中的硅具有阳离子或阴离子亲电性，生成相应的烯醇硅烷或β-酮硅烷。通过控制反应条件，可以控制产品的比例。分别与乙硫醚和环丙硫醚反应生成相应的α，β-环氧硅烷和环丙叉(硅氧基)甲烷衍生物。相反，各种酰基硅烷与α-亚硫基碳负离子(如α-锂硫烷基苯亚砜)反应，得到区域化学纯的烯醇硅烷，这是通过β-硅基-α-氧亚砜中间体中的β-氧与硅的阳离子作用而产生的。产物在这些反应中的选择性取决于硫化物从中间体中离开的能力。在使用硫叶立德的反应中，中性硫化合物在硅迁移之前从甜菜碱中间体中消除，而在与α-亚硫基碳离子的反应中，硅的阳离子亲水性有助于从β-氧亚砜中间体中消除亚硫酸盐离子。另一方面，由环丙基硅烷衍生的环丙基硅烷醇在甲醇中与TsOH进行立体选择性重排生成4-硅基高烯丙基甲醚。含正、S烷基的环丙基硅醇生成E-4-硅基高烯丙基甲醚，含f-丁基的环丙基硅烷生成Z-4-硅基高烯丙基甲醚。E-和Z-4-硅基高烯丙基甲基醚分别与TBAF进行脱硅反应，生成相应的Z-和E-烯烃。在催化量的硼烷-(-)-二苯基羟甲基吡咯烷络合物的催化下，酰基硅烷与硼烷的不对称还原反应生成了具有光学活性的硅醇，产率高，对映体过量高。

Reactions of acylsilanes with sulfur methylides proceed with cationotropy or anionotropy of silicon in the betaine intermediate to give the corresponding enolsilanes or β-ketosilanes. The product's ratio can be controlled by manipulating the reaction conditions. The reaction with sulfur ethylides and that with sulfur cyclopropylide result in the preferential formation of the corresponding α,β-epoxysilanes and cyclopropylidene(siloxy)methane derivatives, respectively. In contrast, various acylsilanes react with α-sulfinyl carbanions such as α-lithioalkyl phenyl sulfoxide to give the regiochemically pure enolsilanes produced by cationotropy of silicon to β-oxygen in the α-silyl-β-oxysulfoxide intermediate. The product's selectivity in these reactions depends on the leaving ability of sulfur compounds from the intermediate. In the reaction using sulfur ylides the elimination of neutral sulfur compound from the betaine intermediate occurs prior to the silicon migration, whereas in the reaction with α-sulfinyl carbanions the cationotropy of silicon assists the elimination of sulfenate ion from the β-oxysulfoxide intermediate.On the other hand, rearrangement of cyclopropylsilylcarbinols derived from cyclopropylacylsilanes with TsOH in methanol proceeds stereoselectively to give 4-silylhomoallyl methyl ether. The cyclopropylsilylcarbinols bearing n- or s-alkyl group on the carbinyl carbon produce E-4-silylhomoallyl methyl ethers, and those bearing f-butyl group afford Z-4-silylhomoallyl methyl ethers. E- and Z-4-silylhomoallyl methyl ethers are protiodesilylated with TBAF to yield the corresponding Z- and E-olefins, respectively.The asymmetric reduction of acylsilanes, in the presence of catalytic amounts of borane-(-)- diphenylhydroxymethyl pyrrolidine complex, with borane leads to the corresponding optically active silylcarbinols in quantitative chemical yield and in high enantiomeric excess.