Ag（I）和KF共催化炔基硅與二醋酸碘苯的反應

王峰　鄧桂勝

摘 要 在Ag（I）和KF共催化下，炔基硅與二醋酸碘苯在30 ℃反應，生成α-乙酰氧基酮，產率29%～78%.這是由炔基硅合成α-乙酰氧基酮的有效改進方法，具有操作簡單和反應條件溫和的特點.

關鍵詞 炔基硅；二醋酸碘苯；α-乙酰氧基酮；醋酸銀；氟化鉀

A survey of solvents indicated that the reaction is sensitive to the reaction medium. For example， silver acetate and KF-cocatalyzed reaction in wet THF， 1，2-dimethoxyethane （DME） and Et2O afforded the desired product 3a in poor yield because of the formation of unknown by-product （Tab.1， entries 12-14）. Moderate yields were obtained when wet DMF was chosen as solvent （Tab.1， entry 15）. The yields were low because of poor reactivity in 1，4-dioxane， CH2Cl2， toluene and EtOAc （Tab.1， entries 16-19）. Among all solvents investigated， wet acetonitrile proved to be optimal for the reaction.

aAll reactions were performed by using trimethyl（phenylethynyl）silane （0.5 mmol） and PhI（OAc）2 （0.5 mmol） in solvent （4 mL） at 30 ℃ for 24 h. bReaction was carried out in the solvent containing 1% water. cIsolated yields. d By-product was observed.

With this optimization study， the substrate scope for synthesis of α-acetoxy ketones 3 is illustrated utilizing various functionalized alkynyltrimethylsilanes. These results were summarized in Tab.2. The use of phenylethynyltrimethylsilane as a substrate gave α-acetoxy acetophenone in 78% yield （Tab.2， entry 1）. When trimethyl（arylethynyl）silanes bearing electron-rich or electron-deficient groups， such as alkyl， alkoxy and halo at the 3 or 4-position of benzene ring were employed as substrates， the reaction gave rise to the corresponding product 3 in lower yields in similar or even longer reaction time （Tab.2， entries 2-7）. The reaction of trimethyl（alkylethynyl）silanes， such as hex-1-ynyltrimethylsilane 1h also afforded desired product 3h in 38% isolated yield （Tab.2， entry 8）， however， the reactivity is lower than that of trimethyl（arylethynyl）silanes. Additionally， a variety of trimethylsilanes derived from 1-propyne derivatives， such as propynyl ether or amine， were transformed to the corresponding products in 33（52% yields （Tab.2， entries 9-12）. In addition， 1，4-bis（3-（trimethylsilyl） prop-2-ynyloxy）benzene 1m derived from the corresponding alkyne with two terminal acetylenic bonds is also a suitable substrate although the yield is very low （Tab.2， entry 13）. PhI（OAc）2 （2 equiv） only reacted with one of the two triple bonds， yielding α-acetoxy ketone 3m with one triple bond intact as unique product without α，α′-diacetoxy diketone 4. In contrast with the result obtained using the above-described substrate 1m， Ag（I） activated-reaction of the alkyne 5 with two terminal acetylenic bonds afforded α-acetoxy ketone 3m and α，α′-diacetoxy diketone 4 without selection （Scheme 1）. Moreover， the reaction showed tolerance towards the internal carbon-carbon triple or double bond （Tab.2， entries 9 and 10）.