查询词典 ketenes

Ketenes, notably dimethyl ketene, readily undergo oligomerization and polymerization

烯酮，特别是二甲基烯酮，很容易齐聚和聚合。

Because of their strong nucleophility of NHCs, the asymmetric Staudinger reaction between ketenes and imines catalyzed by chiral NHC was achieved, gave -lactams with excellent enantioselectivities.

中文摘要我们组利用氮杂环卡宾的亲核性，成功地实现了氮杂环卡宾催化的烯酮与亚胺的Staudinger反应。

In the second part of this thesis, a formal [2+2] cycloaddition ketenes and dialkyl azodicarboxylates was studied. We found that by adjusting the substituents in the diazenes, the reaction mode can be completely switched, and furnish four-membered-ring products, aza-b-lactams, the enantioselectivity was up to 91%.

经研究发现，通过对偶氮化合物取代基团的改变，我们可以实现[4+2]环加成反应到[2+2]环加成反应的转变，在手性氮杂环卡宾的作用下，对具有各种取代基的烯酮都可以很好的产率得到氮杂b-内酰胺，其对映选择性最高可以达到91%。

As open-chain hydroxy aldehydes and hydroxyl ketenes, the monosaccharides are very reactive.

以开链的羟基醛和羟基酮形式存在的单糖非常活泼。

In the first part of this thesis, a formal [4+2] cycloaddition of ketenes with N-benzoyldiazenes catalyzed by chiral NHCs was studied, which gave 1,3,4-oxadiazin-6-ones in very high yields and enantioselectivites.

论文的第一部分内容是在手性氮杂环卡宾的催化下，烯酮与N-苯甲酰偶氮化合物的环加成反应，合成各种手性的噁二嗪酮，它们还可以经过简单的两步一锅法制备手性氨基酯。

According to the results of the examination, the stronger the electron-withdrawing protective group of imines, the better the cis-selectivity of the reaction, 68% yield, trans:cis is 99:1 diastereoselectivity could be leaded by Ts-imines (4-methyl-N-methylene-benzenesulfonaides) with a substituent [2,4-(CH3O)2C6H3], Substrate scope investigation revealed that a wide variety of ketenes and imines could react smoothly to afford corresponding,β-lactams.

实验结果表明，亚胺的保护基团吸电子能力越强，越有利于顺式产物的生成。对甲苯磺酰基保护的取代基为2，4-二甲氧苯基的亚胺参与的该反应可得到68%的产率，反式：顺式=99：1的非对映选择性。底物拓展过程中发现Staudinger反应适用于多种不同的亚胺与烯酮。

Its reaction with ketenes generated in situ from acid chlorides afforded-4--azetidin-2-one, thus provided a 14-member library of-4--azetidin-2-one with yields 76～91% and an excellent stereoselectivity.

我们从PEG支载的苯甲醛出发，经腙的制备及其氯代之后，在三辛胺作用下，由氯代腙原位生成的腈亚胺与亚胺发生[3+2]偶极环加成反应，得到PEG支载四芳基-4，5-二氢-1，2，4-三氮唑衍生物。

The split between the two groups can hardly be papered over.

这两个团体间的分歧难以掩饰。

This approach not only encourages a greater number of responses, but minimizes the likelihood of stale groupthink.

这种做法不仅鼓励了更多的反应，而且减少跟风的可能性。