氧釩錯合物催化共軛加成及硫縮醛化反應之研究
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2009
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第一章部份，我們報導了一種新的三氟甲磺酸氧釩VO(OTf)2催化系統，當應用於醛和酮類化合物的硫縮醛化反應 (thioacetalization)，以及縮醛類化合物 (acetals) 的交換硫縮醛化反應 (transthioacetalization) 時，對於羰官能基有很高的化學選擇性，例如醛基相對於酮基、烯酮基相對於酮基等；而且與羥基 (hydroxy)、烷氧基 (alkoxy)、醯氧基 (acyloxy)、鹵化物 (halide)、胺基 (amino)、硝基 (nitro)、酸 (acid) 和酯 (ester) 等官能基，亦俱備了多元化的相容性。除了反應可在室溫下溫和地進行外，VO(OTf)2催化劑用量大都小於10 mol%，而且可以直接使用硫醇 (thiols) 或二硫醇 (dithiols) 當作親核劑反應物，這些結果均優於一般常用的布忍斯特酸 (Brønsted acids) 或路易斯酸 (Lewis acids) 催化劑，這也揭示了對於有機合成化學將有很大的應用性與實用性。此外，苯甲醛的二硫縮醛化合物的去保護基研究，經運用我們的Ac2O/VO(OTf)2催化系統在無溶劑條件下，可直接轉換為苯甲醛的二乙酸酯 (diacetate，acylal) 化合物，亦是另一項有趣的結果。
第二章部份，我們首次報導了使用三氟甲磺酸氧釩VO(OTf)2催化劑，來促進(hetero)Michael addition反應，以形成C-X和C-C鍵的成功範例。反應性較大的含硫親核劑，進行thia-Michael addition時可獲得很高的產率，而且與羥基 (hydroxy)、烷氧基 (alkoxy)、鹵化物 (halide)、嘧啶基 (pyrimidyl) 等官能基均有很好的相容性。反應性較弱的含氧、含氮親核劑，例如醇 (alcohols)、醯胺 (amides) 和磺酸鹽 (sulfonates) 等，亦可直接進行oxa-及aza-Michael addition反應。此外，氫膦化合物 (hydrogen phosphines) 和氫亞磷酸鹽 (hydrogen phosphites) 等含磷親核劑，在VO(OTf)2催化下亦能成為很有用的phospha-Michael addition的Michael donor；其中全新發展出來的同步、自動 (in situ) 生成的乙醯亞磷酸鹽 (acetylphosphite)，經過VO(OTf)2催化劑活化後，可與α,β-烯酮化合物 (α,β-enones) 進行共軛加成反應。最後，在相同催化條件下，各種富含電子的 (雜環)芳族烴和α,β-不飽和羰基化合物，亦均能有效地進行Friedel- Crafts-type conjugate addition以形成碳－碳鍵，而且其反應步驟非常簡單、易操作。
In the first part, a series of thiols and dithiols has been examined as protic nucleophiles for double nucleophilic condensations with aldehydes, ketones, and acetals catalyzed by amphoteric, water-tolerant vanadyl triflate under mild and neutral conditions. A preliminary study for catalytical acylative dethioacetalization in neat acetic anhydride has also been examined. The newly developed C-S bond formation and scission protocols were carried out smoothly in good to high yields in a highly chemoselective manner. In the second part, a series of thiols, alcohols, carbamates, amides, N-tosyl amides, hydrogen phosphines/phosphites, and (hetero)arenes has been examined as nucleophiles for (hetero)Michael-type additions to enones and enamides catalyzed by amphoteric vanadyl triflate under mild and neutral conditions. The newly developed C-S, C-O, C-N, C-P, and C-C bond formation protocols were carried out smoothly in good to high yields without intervention of any 1,2-additions.
In the first part, a series of thiols and dithiols has been examined as protic nucleophiles for double nucleophilic condensations with aldehydes, ketones, and acetals catalyzed by amphoteric, water-tolerant vanadyl triflate under mild and neutral conditions. A preliminary study for catalytical acylative dethioacetalization in neat acetic anhydride has also been examined. The newly developed C-S bond formation and scission protocols were carried out smoothly in good to high yields in a highly chemoselective manner. In the second part, a series of thiols, alcohols, carbamates, amides, N-tosyl amides, hydrogen phosphines/phosphites, and (hetero)arenes has been examined as nucleophiles for (hetero)Michael-type additions to enones and enamides catalyzed by amphoteric vanadyl triflate under mild and neutral conditions. The newly developed C-S, C-O, C-N, C-P, and C-C bond formation protocols were carried out smoothly in good to high yields without intervention of any 1,2-additions.
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氧釩錯合物, 催化, 硫縮醛化反應, 共軛加成反應, vanadyl triflate, catalysis, thioacetalization, conjugate addition