Three-membered ring systems reactions

To summarize under favorable conditions the acidity of a-hydrogens facilitates the generation of a-sulfoxy and a-sulfonyl carbanions in thiirane and thiirene oxides and dioxides as in acyclic sulfoxides and sulfones. However, the particular structural constraints of three-membered ring systems may lead not only to different chemical consequences following the formation of the carbanions, but may also provide alternative pathways not available in the case of the acyclic counterparts for hydrogen abstraction in the reaction of bases. 

Actually, thiirane dioxides (17) have so far never been isolated in these reactions cis- and trans-olefins were the main products, and all attempts to obtain the three-membered ring system and prevent the loss of SO 2 failed. Hence, the method can be used only for the in situ formation of intermediates. 

The Chemistry of Heterocyclic Compounds has been published since 1950 under the initial editorship of Arnold Weissberger, and later, until his death in 1984, under the joint editorship of Arnold Weissberger and Edward C. Taylor. In 1997, Peter Wipf joined Prof. Taylor as editor. This series attempts to make the extraordinarily complex and diverse held of heterocyclic chemistry as organized and readily accessible as possible. Each volume has traditionally dealt with syntheses, reactions, properties, structure, physical chemistry, and utility of compounds belonging to a specihc ring system or class (e.g., pyridines, thiophenes, pyrimidines, three-membered ring systems). This series has become the basic reference collection for information on heterocyclic compounds. 

Acylation with cyclopentenyl- or cyclohexenylacetyl chloride gave three-membered ring systems.113 114 An interesting example is the reaction of ethylene with acid chlorides complexed with excess A1C13 to give the 17 p.y-unsaturated ketones 115... 

The three-membered ring system, although the most highly strained of all the ring sizes, is readily formed in the cyclisation step. This arises from the fact that carbon-carbon bond formation in this case is an irreversible intramolecular S 2 displacement of halogen reaction, which is facilitated by the thermodynamically favourable anti-periplanar conformation of the anion. 

The reaction of germylene 134 with /< rt-butylphosphaalkyne gave germadiphosphacyclobutene 33, possessing both two- and three-coordinated phosphorus atoms. It was assumed that the reaction started with the addition of 134 to the phosphaalkyne to afford a three-membered ring system. Cyclodimerization of this intermediate yielded the final product 33 (Scheme 49) <2001CC215>. 

One of the most fascinating reaction modes of disilenes is the ready formation of disiliranes, three-membered ring systems containing two silicon atoms and one heteroatom in the ring, which are hardly accessible by other routes. They are mostly formed by [2 + 1] cycloadditions of atoms or molecular fragments to the Si=Si double bond. One of the few examples of other accesses to this ring system is the reaction of AMithio-2,4,6-trimethylanilide 53 with the disilane 52, which affords the azadisilacyclopropane 54 in modest yield (equation 8)75. 

In contrast, aliphatic azides (R = PhCH2, Me3SiCH2) seem to participate in an initial [2 + 1] cycloaddition to give 66, from which nitrogen is subsequently eliminated to leave the three-membered ring system 67 (equation 12a). The reaction of 9 with trimethylsilyl azide furnishes an azadisilacyclopropane of the type 67 as the only isolated product (equation 12b)85. 

This review covers the chemical literature on epoxides and aziridines for the year 2007. As in previous years, this review is not comprehensive but rather covers a selection of synthetically useful and interesting reactions. Three-membered ring systems, epoxides and aziridines in particular, are excellent synthetic intermediates. This is largely due to their ability to be converted into other functional groups such as diols, diamines, and amino alcohols to name but a few. The chapter has been divided into two sections, one covering epoxides and the other covering aziridines. Each of these sections has been further divided into two additional sections, one on the synthesis of the heterocycle and one on the reactions of the heterocycle. There is some overlap between methods for the synthesis of epoxides and aziridines and any overlap has been noted in the text. 

Until now, there was only one example of a cyclotristannene—tetrakis(tri-fert-butyl-silyl)cyclotristannene 20 reported by Wiberg and coworkers in 1999 . The tide compound 20 was prepared by the reaction of t-Bu3SiNa with stable stannylenes Sn[N(SiMe3)2]2 or Sn(OBu-f)2 in pentane at room temperature (Scheme 7). It was isolated as dark, red-brown crystals in 27% yield. In agreement with the symmetrical structure of the molecule, 20 exhibits only two sets of signals in the H, and Si NMR spectra. The most important and informative was the Sn NMR spectrum, which showed both up-field (—694 ppm) and down-field (412 ppm) resonances. The last one is typical for the three-coordinated doubly-bonded tin atoms , whereas the first one can be assigned to an endocyclic Sn atom in a three-membered ring system . ... 

Formation of three-membered-ring systems can also be the result of a nucleophilic addition leading to a zwitterionic intermediate, followed by loss of nitrogen. In these cases, the reactions are related to the addition of sulfur or phosphorus ylides to Michael acceptors. ... 

Hydrozirconation of phospha-alkenes has given the three-membered ring system (163). Addition of dicyclohexyl-borane to the phospha-alkene PhP=CHNMe2 results in the dimeric system (164), and in its reaction with an ethylsiloxane reagent, this phospha-alkene gives a mixture of aminomethyl-... 

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