巴頓-麥康比去氧反應

巴頓-麥康比去氧反應是一個有機反應。在反應中，有機化合物中的羥基被氫取代^[1]^[2]。該反應以英國化學家德里克·巴頓（1918年－1998年）和斯圖爾特·W·麥康比命名。

這個反應是一個自由基取代反應。在另一個類似的反應巴頓脫羧反應中，底物為羧酸。

機理[編輯]

反應機理包括催化劑的自由基引發階段（鏈引發）與後續的鏈轉移階段^[3]。醇1首先反應生成黃原酸酯2。另一個反應物三丁基錫烷3在AIBN8的作用下分解，生成三丁基錫自由基4。這個自由基從2中奪取黃原酸基團，得到烷基自由基5和三丁基錫烷黃原酸酯7。7中的硫－錫鍵很穩定，為反應提供了驅動力。之後自由基5從另一個三丁基錫烷分子中奪取一個氫，生成脫除氧的目標產物6和自由基4，後者繼續參與鏈轉移過程，如下圖所示。

變化[編輯]

其它的氫給予體[編輯]

本反應中使用的三丁基錫烷有較強的毒性，價格昂貴，而且難以從反應體系中分離。這成為了這個反應的主要缺點。一種改良的方法是用氧化（雙）三丁基錫提供自由基，而用聚甲基矽氧烷（英語：Polymethylhydrosiloxane）提供氫^[4]。在這個反應中，硫代氯甲酸苯酯最終生成羰基硫。

三烴基硼烷[編輯]

三烴基硼烷水合物（如帶有很少量水的三甲基硼烷）是另一個很好的氫給予體^[5] 。

在一個催化循環中，在水的存在下，三烴基硼烷3首先被空氣氧化，同時生成甲基自由基4。4與黃原酸酯2作用，生成硫代S-酸酯7與烴基自由基5。化合物3為5提供氫，得到去氧產物與一個新的甲基自由基。

理論計算表明，硼烷水合物中的氫－氧鍵發生均裂時，需要吸熱。所吸收的熱量與三丁基錫烷發生均裂時相近，但比水均裂時吸收的能量要少得多。

參考文獻[編輯]

^ Barton, Derek H. R.; McCombie, Stuart W. A new method for the deoxygenation of secondary alcohols. Journal of the Chemical Society, Perkin Transactions 1 (Royal Society of Chemistry (RSC)). 1975, (16): 1574. ISSN 0300-922X. doi:10.1039/p19750001574.
^ Crich, David; Quintero, Leticia. Radical chemistry associated with the thiocarbonyl group. Chemical Reviews (American Chemical Society (ACS)). 1989, 89 (7): 1413–1432. ISSN 0009-2665. doi:10.1021/cr00097a001.
^ Forbes, J.E.; Zard, S.Z. A novel radical chain reaction of xanthic anhydrides. Further observations on the intermediacy of alkoxy-thiocarbonyl radicals in the Barton-McCombie reaction. Tetrahedron Letters (Elsevier BV). 1989, 30 (33): 4367–4370. ISSN 0040-4039. doi:10.1016/s0040-4039(00)99362-6.
^ Jordi Tormo and Gregory C. Fu (2004). "Tributylstannane (Bu3Snh)-Catalyzed Barton-Mccombie Deoxygenation Of Alcohols: 3-Deoxy-1,2:5,6-Bis-O-(1-Methylethylidene)-Α-D-Ribo-Hexofuranose". Org. Synth. 10: 240.
^ Spiegel, David A.; Wiberg, Kenneth B.; Schacherer, Laura N.; Medeiros, Matthew R.; Wood, John L. Deoxygenation of Alcohols Employing Water as the Hydrogen Atom Source. Journal of the American Chemical Society (American Chemical Society (ACS)). 2005, 127 (36): 12513–12515. ISSN 0002-7863. doi:10.1021/ja052185l.
^ Veitch, Gemma E.; Beckmann, Edith; Burke, Brenda J.; Boyer, Alistair; Maslen, Sarah L.; Ley, Steven V. Synthesis of Azadirachtin: A Long but Successful Journey. Angewandte Chemie International Edition (Wiley-Blackwell). 2007-10-08, 46 (40): 7629–7632. ISSN 1433-7851. doi:10.1002/anie.200703027.
^ Liu, Wen-Cheng; Liao, Chun-Chen. The first total synthesis of (±)-pallescensin B. Chemical Communications (Royal Society of Chemistry (RSC)). 1999, (2): 117–118. ISSN 1359-7345. doi:10.1039/a808714h.
^ Allais, Florent; Boivin, Jean; Nguyen, Van Tai. Part 2. Mechanistic aspects of the reduction of S-alkyl-thionocarbonates in the presence of triethylborane and air. Beilstein Journal of Organic Chemistry (Beilstein Institut). 2007, 3 (1): 46. ISSN 1860-5397. doi:10.1186/1860-5397-3-46.

外部連結[編輯]

organic-chemistry.org上的巴頓-麥康比反應（頁面存檔備份，存於互聯網檔案館）
化學化工新聞關於烴基硼烷的文章（頁面存檔備份，存於互聯網檔案館）

[1] Barton, Derek H. R.; McCombie, Stuart W. A new method for the deoxygenation of secondary alcohols. Journal of the Chemical Society, Perkin Transactions 1 (Royal Society of Chemistry (RSC)). 1975, (16): 1574. ISSN 0300-922X. doi:10.1039/p19750001574.

[2] Crich, David; Quintero, Leticia. Radical chemistry associated with the thiocarbonyl group. Chemical Reviews (American Chemical Society (ACS)). 1989, 89 (7): 1413–1432. ISSN 0009-2665. doi:10.1021/cr00097a001.

[3] Forbes, J.E.; Zard, S.Z. A novel radical chain reaction of xanthic anhydrides. Further observations on the intermediacy of alkoxy-thiocarbonyl radicals in the Barton-McCombie reaction. Tetrahedron Letters (Elsevier BV). 1989, 30 (33): 4367–4370. ISSN 0040-4039. doi:10.1016/s0040-4039(00)99362-6.

[4] Jordi Tormo and Gregory C. Fu (2004). "Tributylstannane (Bu3Snh)-Catalyzed Barton-Mccombie Deoxygenation Of Alcohols: 3-Deoxy-1,2:5,6-Bis-O-(1-Methylethylidene)-Α-D-Ribo-Hexofuranose". Org. Synth. 10: 240.

[5] Spiegel, David A.; Wiberg, Kenneth B.; Schacherer, Laura N.; Medeiros, Matthew R.; Wood, John L. Deoxygenation of Alcohols Employing Water as the Hydrogen Atom Source. Journal of the American Chemical Society (American Chemical Society (ACS)). 2005, 127 (36): 12513–12515. ISSN 0002-7863. doi:10.1021/ja052185l.

[6] Veitch, Gemma E.; Beckmann, Edith; Burke, Brenda J.; Boyer, Alistair; Maslen, Sarah L.; Ley, Steven V. Synthesis of Azadirachtin: A Long but Successful Journey. Angewandte Chemie International Edition (Wiley-Blackwell). 2007-10-08, 46 (40): 7629–7632. ISSN 1433-7851. doi:10.1002/anie.200703027.

[7] Liu, Wen-Cheng; Liao, Chun-Chen. The first total synthesis of (±)-pallescensin B. Chemical Communications (Royal Society of Chemistry (RSC)). 1999, (2): 117–118. ISSN 1359-7345. doi:10.1039/a808714h.

[8] Allais, Florent; Boivin, Jean; Nguyen, Van Tai. Part 2. Mechanistic aspects of the reduction of S-alkyl-thionocarbonates in the presence of triethylborane and air. Beilstein Journal of Organic Chemistry (Beilstein Institut). 2007, 3 (1): 46. ISSN 1860-5397. doi:10.1186/1860-5397-3-46.

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