【作者】 张方林；

【导师】 龚跃法；

【作者基本信息】 华中科技大学 ， 无机化学， 2008， 博士

【摘要】 不对称羟醛缩合反应是有机合成中立体选择性地形成碳碳键的最重要方法之一。近年来,有机小分子已经被证实可以有效地催化醛酮的直接羟醛缩合反应。迄今为止,反应底物醛的选择范围依然狭小,有关高活性醛或含官能团的醛的羟醛缩合反应的研究很少,而此类羟醛缩合反应产物是一类多官能团化合物,应用广泛。在本论文中,我们研究了在脂环仲胺催化下脂肪醛酮与高活性醛或3-邻苯二甲酰亚胺基丙醛间的交叉羟醛缩合反应。鉴于α-三氯甲基醇是应用广泛的中间体,其中β-三氯甲基-β-羟基醛能容易地转化成生物活性的化合物与天然产物,论文第二章研究了三氯乙醛与简单脂肪醛间的交叉羟醛缩合反应。通过筛选反应溶剂与有机催化剂发现哌啶和L-脯氨酰胺可以有效催化交叉羟醛缩合,并抑制了脂肪醛的自身缩合反应。事实上,等摩尔的简单脂肪醛与三氯乙醛在30%的哌啶催化下反应能获得产率高达87%的β-三氯甲基-β-羟基醛118。另外,L-脯氨酰胺催化的反应,除了可以获得产率高达95%的118,其ee值最高也可达到88%。利用酵母直接还原手性118a(ee值80%)可得到更高对映选择性的1,3-二醇化合物122a(ee值高达95%)。由于α-三氟甲基醇化合物在药物以及功能材料等领域的广泛应用,建立其有效的合成方法已成为人们关注的一个课题。β-三氟甲基-β-羟基酮的合成一般是通过酮预先形成的烯胺或烯醇硅醚与三氟乙醛乙基半缩醛反应得到。论文第三章主要探讨了脂环仲胺催化下三氟乙醛乙基半缩醛与脂肪醛酮的直接羟醛缩合反应。首先,以三氟乙醛乙基半缩醛与环己酮的直接羟醛缩合反应为模型,通过GC跟踪反应过程,考查了各脂环仲胺的催化活性及反应历程。结果表明,四氢吡咯的催化效果最好,催化活性明显高于哌啶。同时还观察到:1)、四氢吡咯与三氟乙醛乙基半缩醛几乎完全形成氨基半缩醛,氨基半缩醛在羟醛缩合反应的初期含量不变,其含量在三氟乙醛乙基半缩醛消失后才缓慢下降;2)、羟醛缩合产物138b的anti/syn的比值随时间变化,在反应的初期产物以anti为主,而到反应的末期则是syn产物为主;3)、反应过程中四氢吡咯可以与酮反应生成的烯胺中间体不过其浓度相当的低。通过分析上述实验结果,我们认为烯胺的形成速率是羟醛缩合反应进行的决速步。不仅环酮及直链脂肪酮而且芳香酮及脂肪醛都可以在四氢吡咯催化下与三氟乙醛乙基半缩醛顺利进行羟醛缩合反应,并都得到良好产率的羟醛缩合产物。经比较所有使用的酮,发现环戊酮的活性最高,而有意思的是,低催化活性的哌啶也能催化高反应活性的环戊酮与三氟乙醛乙基半缩醛顺利进行直接羟醛缩合反应。最后,初步研究了L-脯氨酰胺催化下三氟乙醛乙基半缩醛与环己酮的不对称羟醛缩合反应,羟醛缩合产物138b能以92%的产率获得,其对映选择性达到88%。鉴于L-脯氨酰胺催化三氯乙醛及三氟乙醛乙基半缩醛的直接羟醛缩合反应可获得高对映选择性的产物,是否也能有效催化同为高活性醛的乙醛酸酯与脂肪醛酮间的反应?论文第四章对此进行了探索。考虑到乙醛酸酯与α位有取代基的脂肪醛的直接交叉羟醛缩合反应未见报道,并且产物容易衍生得到泛内酯、泛内酰胺,我们重点研究了在L-脯氨酰胺催化下乙醛酸苄酯与异丁醛间的不对称交叉羟醛缩合反应,发现能以93%的高产率得到ee值为52%的羟醛缩合产物151。通过一步还原氨化,151很容易的转化成药物中间体N-苯基泛内酰胺。论文第五章研究了L-脯氨酸催化β-氨基醛的不对称羟醛缩合反应,并在此基础上建立了一种合成光学活性的双环哌啶化合物的方法。首先,详细研究了L-脯氨酸催化下3-邻苯二甲酰亚胺基丙醛与丙酮及环酮间的不对称交叉羟醛缩合及Mannich反应,发现与环酮的反应可以得到产率良好的交叉羟醛缩合产物171,其ee值都高于99%。通过对路线及反应条件的筛选,最佳合成双环哌啶化合物176的方法是:羟醛缩合产物171先用过量的硼氢化钠还原,再在醋酸中回流,获得的氨基醇直接与苯甲酰氯反应,得到氨基选择性被保护的化合物180,所得180与对甲苯磺酰氯反应选择性地磺酰化,得到化合物181,随后181用氢化钠处理后得到关环产物182,化合物182在氢氧化钠水溶液中回流水解得到双环哌啶化合物176,四步总产率为18%。双环哌啶化合物176催化直接羟醛缩合反应的活性研究还在进行之中。更多还原

【Abstract】 The asymmetric aldol reaction is one of the most important methods of forming carbon-carbon bonds. It has been known that small organic molecules can catalyze the direct aldol reaction between aldehydes or between aldehyde and ketone. However, the substrate scope of this catalytic reaction is still narrow up to now. There are few reports refered to the aldol reaction converned on reactive or functionalized aldehydes, although the aldol products with various functional groups are very useful. In this thesis, the cross aldol reactions of aliphatic ketones or aldehydes with reactive aldehydes or 3-phthalimidopropanal were studied by using alicyclic secondary amines as catalysts.In view ofα-trichloromethyl alcohols, especiallyβ-trichloromethyl-β-hydroxy aldehydes are easily converting into biologically important compounds and natural products, in the second part of the thesis, direct catalytic cross aldol reaction of chloral with aliphatic aldehydes was investigated. Through screening the organocatalysts in different solvents, we found that both piperidine and L-prolinamide are the efficient catalysts for the cross aldol reaction, while the competitive self-aldol reacrion of aliphatic aldehyde is markedly restrained. In fact, in the presence of 20 mol% of piperidine, the cross aldol reaction undergoes smoothly when equimolar amounts of aliphatic aldehyde and chloral are used, givingβ-trichloromethyl-β-hydroxy aldehydes in high yield (up to 87%). In the case of L-prolinamide, the aldol products 118 were isolated in up to 95% yield with 88% ee. In addition, the baker’s yeast mediated reduction of chiral 118a (80% ee) underwent smoothly and afforded the higher enantioselective primary alcohol 122a (95% ee).Due to the usefulness ofα-trifluoromethylated in drugs and materials, it becomes an interesting task to search for a suitable approach to such compounds for synthetic chemists. The synthesis ofβ-hydroxy-β-trifluoromethyl ketones was commonly performed through the reaction of trifluoroacetaldehyde ethyl hemiacetal with enamines or silyl enolates. In the third part of the thesis, we described that the direct aldol reaction of trifluoroacetaldehyde ethyl hemiacetal with ketones or aldehydes catalyzed by alicyclic secondary amines. Chosing the aldol reaction of trifluoroacetaldehyde ethyl hemiacetal with cyclohexanone as a model system, the catalytic reactivity of secondary amines was investigated and the reaction progress was followed by GC analysis. The results clearly demonstrated that pyrrolidine was an appropriate catalyst for this reaction and the catalytic reactivity of pyrrolidine was much higher than piperidine. Three interesting phenomena were also observed. 1) the concentration of hemiaminal formed in situ was almost kept constant at the initial stage, and started to decrease slowly when the hemiacetal was completely consumed. 2) the reaction preferentially gave anti-138b initially, and was gradually converted in situ into syn-138b during the reaction. 3) the concentration of the catalyst and the enamine intermediates were kept extremely low during the reaction. Based on these observations, we suggested that formation of the enamine would be a rate-determining step for the catalytic aldol reaction.Pyrrolidine-catalyzed aldol reaction of trifluoroacetaldehyde ethyl hemiacetal with other ketones such as linear aliphatic ketones, alicyclic ketones and aromatic ketones as well as aliphatic aldehydes were tested under similar conditions and the reaction proceeded smoothly to afford the aldol products in good yields. Among all the ketones, cyclopentanone was the most reactive. In fact, piperidine, a poor catalyst, can effectively catalyze the aldol reaction of hemiacetal with cyclopentanone. In addition, the asymmetric aldol reaction of trifluoroacetaldehyde ethyl hemiacetal with cyclohexanone catalyzed by L-prolinamide was also discussed. The aldol product 138b was afforded in 92% yield with high enantioselectivity (88% ee).Since L-prolinamide was an efficient catalyst for the direct cross aldol reactions of chloral or fluoral, in the fourth part of the thesis, we continued to explore the cross aldol reaction of another reactive aldehyde, glyoxylate with aliphatic ketones and aldehydes. For the direct cross aldol reaction of glyoxylate with branched aldehydes was not reported hitherto and the cross adduct was easily converted into pantolactone and pantolactam. The L-prolinamide catalyzed asymmetric cross aldol reaction of benzyl glyoxylate with isobutanal was investigated, and afforded the cross adducts 151 in good yield (93%) with moderate enantioselectivity (52%). The aldol product 151 was easily converted into pantolactam in high yield through a reductive amination.In the fifth part of the thesis, base on the observations for the L-proline catalyzed asymmetric aldol reaction ofβ-amino aldehyde, we have developed a highly enantioselective approach for preparing optically active bicyclic piperidines. The L-proline catalyzed asymmetric aldol or Mannich reaction of 3-phthalimidopropanal with aliphatic ketones was investigated in details. The cross adducts 171 were afforded in good yields in the reactions with alicyclic ketones. A high enantioselectivity up to 99 % ee was also observed. Then, the possible synthetic routes and the reaction conditions were evaluated, and a workable synthetic route to the target bicyclic 4-hydroxypiperidine 176 was found. After treating 171 with excess NaBH4, the reduction mixture was heated in acetic acid at 80 oC. The obtained amino alcohol was further benzoylated without isolation with benzoyl chloride, affording the desired amino protective product 180. When the tosylation of 180 was performed with tosyl chloride, almost only the desired tosylates 181 was given. Subsequent cyclization carried out by treatment with NaH produced 182. Deprotection of 182a was achieved by refluxing in NaOH aqueous solution, and the target bicyclic 4-hydroxypiperidine 176a obtained in 18% overall yield. The application of 176 to the catalytic direct aldol reaction is underway.更多还原