CONFORMATIONAL AND MEDIUM EFFECTS ON INTRAMOLECULAR CARBENE REACTIONS
CONFORMATIONAL AND MEDIUM EFFECTS ON INTRAMOLECULAR CARBENE REACTIONS
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DOI：
10.1021/ja00760a033
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发表时间：
1972-01-01
影响因子：
15
通讯作者：
RANDO, RR
中科院分区：
文献类型：
--
作者：
RANDO, RR
-重氮酰胺的光化学分解导致内酰胺类化合物的分子内形成。因此，W，W-二乙基重氮乙酰胺(1)在二氧六环中的光解生成大致相等的1-乙基-1-4-甲基-1-2-氮杂二酮(2)和1-乙基-2-吡咯烷酮(3)。在这些反应中观察到了显著的溶剂效应。随着介质极性的增加，JS-内酰胺/γ-内酰胺的比例增大，较好地了解了结构和电子态对卡宾反应活性的总体影响。3另一方面，优先构象和溶剂效应的结果不太确定。本报告的目的是指出构象和溶剂对以重氮酰胺为光化学源的卡宾的化学有相当深远的影响。从Closs4和Kirmse的工作可以推断出择优构象对某些卡宾的分子内反应的影响。5这些作者证明了分子内1，3CH插入产生的环丙烷的相对量对各个过渡态的有效拥挤非常敏感。例如，仲丁基锂与二氯甲烷的反应生成的环丙烷是顺式环丙烷的约九倍。4顺式异构体的过渡态当然是比较拥挤的。Kaplan和Meloly6认为，4-重氮-2，2，5，5-四甲基-3-己酮不能进行Wolff重排可以追溯到不利的重氮酮构象。人们感兴趣地注意到，尽管碳氧基卡宾进行了简单的分子间CH插入反应和双键加成反应，3这些反应的分子内对应反应并没有实现。例如，重氮乙酸烯丙酯在环己烷中的光解得到了唯一的产物乙酸烯丙基环己酯。8未发生分子内内酯形成。只有当烷氧基部分具有特别大的体积时，内酯的形成才开始出现，如重氮乙酸叔丁酯。9重氮酯在环己烷中光化学分解生成9.5%的y，-二甲基丁内酯和90.5%的乙酸乙酯。所有这些都表明，在这些反应中的主导因素是
The photochemical decomposition of-diazoamides leads to the intramolecular formation of lactams. Thus, the photolysis of W, W-diethyldiazoacetamide (1) in dioxane produces 1-ethy 1-4-methy 1-2-azetidinone (2) and 1-ethyl-2-pyrollidinone (3) in roughly equal amounts. Striking solvent effects are observed on these reactions. As the polarity of the medium is increased, the ratio of jS-lactam/y-lactam increases.The gross effects of structure and electronic state on the reactivity of carbenes are fairly well under-stood. 3 On the other hand, the consequences of preferred conformations and solventeffects are less certain. It is the purpose of this report to point out rather profound influences of both conformation and solvent on the chemistry of the carbenes photochemically derived from-diazo amides. The influence of preferred conformations on the intramolecular reactions of certain carbenoids can be inferred from the work of Closs4 andKirmse. 5 These authors demonstrated that the relative amounts of cyclopropanes produced by intramolecular 1, 3 CH insertion were quite sensitiveto the effective crowding in the respective transition states. For example, the reaction of sec-butyllithium and methylene chloride leads to the formation of approximately nine times as much írarcs-dimethylcyclopropane as cis-. 4 The tran-sition state on the way to the cis isomer is, of course, the more crowded one. Kaplan and Meloy6 argued that the failure of 4-diazo-2, 2, 5, 5-tetramethyl-3-hex-anone to undergo Wolff rearrangement can be traced to an unfavorable diazo ketone conformation. One notes with interest the fact that although carbalkoxycarbenes undergo facile intermolecular CH insertion7 and double-bond addition reactions, 3 the intramolecular counterparts of these reactions are not achieved. For example, the photolysis of allyl di-azoacetate in cyclohexane affords allyl cyclohexyl-acetate as the sole product. 8 Intramolecular lactone formation does not occur. Lactone formation only starts to come into the picture when the alkoxy moiety is of exceptional bulk, as in tert-butyl diazoacetate. 9 Photochemical decomposition of this diazo ester in cyclohexane affords 9.5% y,-dimethylbutyrolactone along with 90.5% íerí-butyl cyclohexylacetate. All this suggests that the dominant factor in these reactions is