定义Definition
西蒙斯-史密斯反应是用二碘甲烷和锌-铜偶（或二乙基锌）生成的类卡宾试剂 ICH₂ZnI，把烯烃立体专一地转化为环丙烷的反应。亚甲基从双键同一面加上，烯烃原有的顺反关系在产物中保持。
The Simmons–Smith reaction converts alkenes stereospecifically into cyclopropanes using the carbenoid ICH₂ZnI generated from diiodomethane and a zinc–copper couple (or diethylzinc). The CH₂ unit adds to one face of the double bond, so the alkene's cis/trans geometry is retained in the product.
机理Mechanism
锌插入 C–I 键形成碘甲基碘化锌（类卡宾），它不是自由卡宾。试剂与烯烃经“蝴蝶形”协同过渡态把 CH₂ 转移到双键上，同时放出 ZnI₂，因此反应是立体专一的同面加成。
Zinc inserts into a C–I bond to give iodomethylzinc iodide, a carbenoid rather than a free carbene. It transfers CH₂ to the alkene through a concerted ‘butterfly’ transition state while releasing ZnI₂, so the addition is stereospecific and suprafacial.
发现Discovery
1958 年杜邦公司的霍华德·西蒙斯和罗纳德·史密斯报道了这一方法。1966 年古河（Furukawa）用二乙基锌代替锌-铜偶，使反应更易重复、活性更高。
Howard Simmons and Ronald Smith at DuPont reported the method in 1958. In 1966 Furukawa replaced the zinc–copper couple with diethylzinc, making the reaction more reproducible and reactive.
选择性与应用Selectivity and uses
烯丙醇的羟基能与锌配位，把亚甲基导向羟基同侧，得到高非对映选择性。富电子烯烃反应更快。该反应广泛用于合成含环丙烷的天然产物和药物。
The hydroxyl group of an allylic alcohol coordinates zinc and directs CH₂ to the same face, giving high diastereoselectivity. Electron-rich alkenes react faster. The reaction is widely used to make cyclopropane-containing natural products and drugs.
反应Reactions
乙醚或二氯甲烷，室温至回流；或 Et₂Zn/CH₂I₂
Ether or dichloromethane, room temperature to reflux; or Et₂Zn/CH₂I₂
Zn 插入 CH₂I₂ 的 C–I 键，生成 ICH₂ZnI。
Zn inserts into a C–I bond of CH₂I₂ to give ICH₂ZnI.
类卡宾与烯烃经协同过渡态同面加成，形成环丙烷并放出 ZnI₂。
The carbenoid adds suprafacially to the alkene in a concerted step, forming the cyclopropane and ZnI₂.
环己烯转化为降蒈烷。
Cyclohexene gives norcarane (bicyclo[4.1.0]heptane).
年表Timeline
- 1958
西蒙斯与史密斯报道该反应
Simmons and Smith report the reaction
- 1966
古河改进：Et₂Zn/CH₂I₂
Furukawa modification with Et₂Zn/CH₂I₂