In the presence of enantiopure MTBH2
(monothiobinaphthol, 2-hydroxy-2â²mercapto-1,1â²-binaphthyl; 0.2 eq.) quantitative allylation of ArC(O)Me takes place with impure Sn(CH2CHCH2)4
(prepared from allyl chloride, air-oxidised magnesium and SnCl4) to yield tert-homoallylic alcohols in 85â92% ee. In the same process highly purified, or commercial, Sn(CH2CHCH2)4 yields material of only 35â50% ee. The origin of these effects is the presence of small amounts of the compounds, EtSn(CH2CHCH2)3, ClSn(CH2CHCH2)3 ClSnEt(CH2CHCH2)2 in the tetraallyltin sample and the presence of traces of water (which inhibits achiral background reactions). All the triallyl and diallyl species enhance the stereoselectivity in the catalytic allylation reaction, the chlorides more so than the ethyl compound. Hydrolysis of ClSnEt(CH2CHCH2)2 affords crystallographically characterised Sn4(μ3-O)(μ2-Cl)2Cl2Et4(CH2CHCH2)4. Reaction of this latter compound with MTBH2 leads to the most potent catalyst.
在手性纯
MTBH2(单
硫代
苯二醇,2-羟基-2′-巯基-1,1′-联
萘;0.2当量)的存在下,与不纯的Sn(CH2CHCH2)4(由
丙烯氯、空气
氧化镁和SnCl4制备)进行定量的
烯丙基化反应,能够生成含有85–92%光学纯度的叔同
烯丙醇。在同一过程中,高度纯化的或商业化的Sn(CH2CHCH2)4仅产生35–50%的光学纯度。这些效果的来源是
四丙基锡样品中存在少量化合物EtSn(CH2CHCH2)3、ClSn(CH2CHCH2)3以及ClSnEt(CH2CHCH2)2,以及
水的微量存在(抑制了非手性背景反应)。所有的
三烯丙基和
二烯丙基物种都增强了催化
烯丙基化反应中的立体选择性,其中
氯化物的效果优于乙基化合物。ClSnEt(CH2CHCH2)2的
水解反应生成了具有晶体结构特征的Sn4(μ3-O)(μ2-Cl)2Cl2Et4(CH2CHCH2)4。后者与
MT 的反应生成了最强的
催化剂。