Selective mono- and di-allylation and allenylation of chlorosilanes using indium

Allyl and allenyl groups have been introduced into silicon systems by the allylation and allenylation of chlorosilanes using allyl bromide or propargyl bromide with indium. The allylation of chlorosilanes afforded a variety of aryl, aralkyl, and alkenyl substituted allylsilanes. By applying this method, the reactions of 1-bromo-3-methylbut-2-ene, 3-bromo-2-methylprop-1-ene and 3-bromobut-1-ene with chlorosilanes also proceed smoothly to give regioselectively allylic rearrangement products in good yields. Mediated by indium, dichlorosilanes (R₂SiCl₂) and trichlorosilanes (RSiCl₃) can either afford monoallylated silanes or diallylated silanes depending on the amount of allyl bromide and indium used.     

Reaction pathways of zirconocene-catalyzed silylation of alkenes with chlorosilanes

Reaction pathways as well as stereochemistries and stoichiometries of zirconocene-catalyzed silylation of olefins with chlorosilanes in the presence of ⁿBuMgCl were studied and discussed in detail. Rate determining steps were examined by kinetic studies and labeling experiments.     

Titanocene-catalyzed double silylation of dienes and aryl alkenes with chlorosilanes

Double silylation of 1,3-butadienes with chlorosilanes was found to proceed by using titanocene dichloride as the catalyst in the presence of ⁿBuMgCl, giving rise to 1,4-disilylated 2-butenes in good yields. Aryl substituted alkenes also afforded 1,2-disilylated products under similar conditions.     

Hexachloroethane: a highly efficient reagent for the synthesis of chlorosilanes from hydrosilanes

A new and efficient chlorination protocol is presented for the preparation of chlorosilanes from hydrosilanes. A variety of chlorinating agents in combination with palladium(II) chloride as the catalyst are examined. Among them, hexachloroethane is found to be the best choice, furnishing the desired product in good to quantitative yields under mild conditions. Various hydrosilanes are used as starting materials to explore the scope of this reaction.     

钐试剂在有机合成中应用的若干新进展

综述了本课题组最近几年关于钐试剂在有机合成中应用的研究进展. 主要包括以下几部分内容: (1) 二碘化钐促进的有机反应研究; (2) 金属钐直接应用于有机合成的研究; (3) 其它钐试剂 (三碘化钐, 烯丙基溴化钐) 促进的有机反应研究.     

Titanocene-catalyzed formation of allylsilanes from allyl ethers and chlorosilanes

A new method for silylation of allyl ethers with chlorosilanes has been developed by the use of Cp₂TiCl₂ as a catalyst. This reaction proceeds efficiently at −20 °C in THF using ⁿBuMgCl. A plausible reaction pathway via allyltitanocene intermediate was proposed.     

Controlled introduction of allylic chlorines into poly(vinyl chloride)

Colorless poly(vinyl chloride)s (PVC) containing up to 1.6 allylic chlorines per molecule have been prepared by controlled random dehydrochlorination with a strong base. The effect of temperature in the ?50 to +24°C range on the number of allylic chlorines and color of PVC has been investigated by ozonization experiments and UV–visible spectroscopy. A two-parameter kinetic model has been developed which quantitatively accounts for the observations and points the way for further research.     

烯丙基碘和锡与醛的选择加成反应

含活性基团的醛可与烯丙碘和锡粉直接进行亲核加成反应，得到高烯丙基的醇，水的存在不利于此反应的进行，与烯丙基溴相比，烯丙基碘反应活性更强，可在短时间内得较高的产率。     

Influences on the regioselectivity of palladium-catalyzed allylic alkylations

Chelated amino acid ester enolates are excellent nucleophiles for palladium-catalyzed allylic alkylations. These enolates react rapidly at -78 degrees C and in general without isomerization of pi-allyl palladium complexes. Therefore, they are good candidates for mechanistic studies and regioselective reactions. Terminal pi-allyl palladium complexes are preferentially attacked at the least hindered position giving rise to linear products, as illustrated with several (E)-configured allylic substrates. Under isomerization free conditions the branched products are formed preferentially from the corresponding (Z)-allyl substrates. An interesting behavior is observed in the reaction of secondary allylic substrates. Aryl-substituted substrates show a significant memory effect which can be explained by an asymmetric pi-allyl complex. For alkyl-substituted substrates a strong dependence of the regioselectivity on the leaving group is observed, which can be explained by different conformations in the ionization step. Under isomerization free conditions the product ratio gives important information about this step.     

醋酸烯丙酯选择性地合成烯丙基硒醚

醋酸烯丙酯被Pd(PPh3)4-SmI2还原，并发生中间体π-烯丙基钯络合物的极性 反转，而后与芳基硒溴化物作用，生成烯丙基硒醚．     

Zinc mediated propenylation of Baylis-Hillman acetates

Allyl bromide efficiently reacts with Baylis-Hillman acetates in the presence of zinc and copper iodide resulting in substituted 1,5-dienes.     

Enantioselective synthesis of acyclic allylic esters catalyzed by a palladium/BINAP(S) system

The synthesis of chiral nonracemic acyclic allylic pivalates via the Pd-catalyzed allylic substitution of racemic allylic carbonates is presented. Good to excellent enantioselectivities (up to 90%) were observed in several cases. An extraordinarily high preference for the production of the branched regioisomeric product is seen when starting from 3-buten-2-yl and crotyl substrates. A significant kinetic resolution (k_rel = 38) of the 1,3-dimethylallyl substrate was also observed, leading to the production of esters of both enantiomers of an allylic alcohol with a single enantiomer of catalyst.     

Transition metal-free activation of allylic acetates toward regioselective S-allylation of thiols

Allylic acetates have been used as allylating agents under transition metal-free condition toward an economical and sustainable regioselective S-allylation of aromatic and aliphatic thiols in the presence of potassium carbonate in DMF.     

Pd-catalyzed nucleophilic allylic alkylation of aliphatic aldehydes by the use of allyl alcohols

Under catalysis of Pd(OAc)₂-(P-n-Bu)₃, Et₂Zn promotes a variety of allyl alcohols to undergo nucleophilic allylation of aliphatic aldehydes and ketones at room temperature and provides homoallyl alcohols in 60-90 and ca. 60% isolated yield, respectively. The reaction is irreversible and kinetically controlled, and unique regio- and stereoselectivities observed for the allylation with unsymmetrically substituted allyl alcohols are discussed.     

Rapid access to homoallylic alcohols via Pd(OAc)2 catalyzed Barbier type allylation in presence of DMAP

DMAP was found to accelerate significantly the rate of Pd(OAc)₂ catalyzed Barbier type allylation of carbonyl compounds by allylbromide using SnCl₂·2H₂O as reducing agent. Both aldehyde as well as ketones produced excellent yields within a short reaction time in the presence of 3 mol % of Pd(OAc)₂ and 12 mol % of DMAP at room temperature. Aldehydes could be allylated within 5–10 min whereas, in case of ketones, the reaction completes in 45–120 min.