羰基化合物的自由基環合反應之應用與控制的活性自由基聚合反應之研究

Abstract

CHINESE ABSTRACT

本論文包含兩各部份，一為羰基化合物的自由基環合反應之應用，另一為 有控制的活性自由基聚合反應之研究。 在羰基化合物自由基環合反應的研究中，我們探討了四種自由基的環合反應，其中包含α-硫基碳自由基加成到矽基酮，烷基自由基加成到α-含氧基矽基酮，α-錫基碳自由基加成到羰基，α-醯胺基碳自由基加成到矽基酮。在第一章α-硫基碳自由基加成到矽基酮的研究中，我們得到的環合產物與還原產物的比例大約是一比一。其原因在於，反應中產生硫酚。這樣一來，增加了烷基自由基抓氫的速率。另外我們也研究不同氧化態的α-硫基碳自由基的環合反應，但是都沒得到預期的環合產物。 在第二章中，以不同醣類分子如樹膠醛醣，來蘇醣，核醣與甘露醣為起始物所得到的α-含氧基矽基酮被成功的合成出來。α-含氧基矽基酮的製備是利用矽基銅錯合物與醛醣化合物作用得到α-矽基醇，再進一步氧化矽基醇而得到α-含氧基矽基酮。在五員環的自由基環合反應中，我們成功的製備出不同官能基的矽氧基五員碳環。這是第一個在文獻中，能夠把醣類分子轉換成五員碳環，並額外建構出一個醇基或矽氧基的方法。在六員環的自由基環合反應中，我們無法得到環合產物，原因在於反應中，自由基的中間體因為推拉作用的影響而特別穩定。 在第三章中，我們也從樹膠醛醣成功的合成出來環合前驅物，但是在製備的過程中，我們一直無法提高合成的效率，我們歸咎於α-含氧基-三丁基錫基二硫硫酸酯是一個不穩定的官能基。因此我們遭遇到許多合成上的問題。 在第四章中，α-醯胺基碳自由基加成到矽基酮的策略被利用來合成Castanospermine的天然物。在合成的步驟中，我們以較簡短的方法合成出環合前驅物，但是自由基環合反應中，我們得到很低產率的吲哚叻咭啶化合物。

在第二部份(第五章)的有控制的活性自由基聚合反應之研究中，在2,2,6,6-四甲基哌啶-1-氧自由基所調節的苯乙烯聚合反應中，其聚合反應速率可以因為加入添加劑如烷氧胺，而被提高。當添加劑的平衡常數是苯乙烯基-2,2,6,6-四甲基哌啶-1-氧自由基的1000倍時，其轉換率可以增加兩倍，只要加入25%的添加劑就可得到好的效果。另外，我們也利用電腦模擬來支持我們的結果。 第六章中，在有控制的活性自由基苯乙烯聚合反應的研究中，我們開發了一個環增大的烷氧胺99，在扮演起始劑與調節劑的角色中，它展現出比它的類似物84還要有效率。烷氧胺99的平衡常數，是類似物84的 3 倍。這樣的結果，驗證了在環中，加入一個 NH 的好處。

ENGLSIH ABSTRACT

This thesis is divided into two parts, one is the application of radical cyclization reactions of carbonyl compounds, and the other is the study of controlled living radical polymerizations. In the first chapter, the intramolecular cyclization of the α-sulfenyl radical cyclization with acylsilane went through the cyclization-rearrangement-fragmentation pathway to afford silyl enol ethers. Thiophenol, generated from the reaction cycle, enhanced the efficiency of hydrogen abstraction. The best result of the product ratio (silyl enol ethers/ reduction products = 2/1, determined by NMR integration) was obtained by the addition of allyltributyltin as an additive. Unfortunately, α-sulfonyl radical did not cyclize to acylsilanes. Second, we have developed a procedure that could convert carbohydrates to functionalized carbocycles. A successful method to construct α-oxygenated carbohydrate-derived acylsilanes was also explored. Three different acylsilanes, derived from arabinose, lyxose, and ribose were converted to functionalized silyloxy carbocycles. These results are the first examples of radical cyclization reactions of acyclic sugars, which could give one additional hydroxyl group or silylated hydroxyl group on the newly formed carbocyclic rings. 6-Exo cyclization reaction of mannose-derived acylsilane was not successful due to the formation of a particularly stable radical intermediate stabilized by the captodative effect. The cyclization precursor, bearing α-oxygenated tin-xanthate moiety, was also prepared in order to study the 1,3-stannyl shift in carbohydrate system. α-Oxygenated tin-xanthate moiety is a labile functional group during the preparation. The six-membered ring α-acylamino radical precursor accessed from a monosaccharide and a simple saturated aliphatic acylsilane were prepared. Tin-mediated cyclization reaction to construct indolizidinone is not so efficient. Very low yield was obtained. In the second part of this thesis, the styryl-TEMPO-mediated styrene polymerization can be accelerated upon using efficient alkoxyamines as additives. For additives with equilibrium constants that are 3 orders of magnitude larger than K of styryl-TEMPO, an increase of the conversion by about a factor of 2 can be achieved. Good results can be obtained with only 25% of the alkoxyamine additive with respect to styryl-TEMPO. The results are further supported by numerical simulations. We have also showed that the ring-enlarged alkoxyamine 99 is a more efficient initiator/regulator for controlled living radical polymerization of styrene than its lower homologue 84. The equilibrium constant K of 99 is about 3 times larger as compared to the K-value of 84, clearly documenting the benefit of the ring-enlargement by the insertion of an NH moiety.