Intramolecular ring closure reaction

A. Intramolecular Ring-Closure Reactions of Phosphine Ligands. 150... 

Funk RL, Vollhardt KPC (1980) A review on the intramolecular ring closure reactions of o-xylylenes insteroid synthesis, Chem Soc Rev 9 41... 

These results suggest that anion 328 is unable to initiate the process, a reaction that is performed by the enolate ion of acetone. However, the rate of the coupling reaction between the anion of acetone and the radical intermediate formed is slower than the rate of intramolecular ring closure reaction of the radical. 

Scheme 9.4 Problems encountered during opening of typical epoxide intermediate (see also Section 9.4, Chemical Synthesis) when intended N-external ester substituents do not bear alpha-substituents [10]. A Normal, well-behaved reaction as typically deployed for beta-blockers wherein the N-alkyl group bears an alpha-substituent as most commonly represented by isopropylamine. B The over-alky-lation problem that occurs significantly when the N-alkyl group is not alpha-substituted. Also note that when n = 3 or 4, the first alkylation is instead followed immediately by an intramolecular ring-closure reaction to form the five- or six-membered lactam. These unwanted side products, although readily...

Carbodiimides generated in situ in the proximity of a hydroxy group as in 638 undergo intramolecular ring closure reactions to give heterocycles, such as 639. ... 

Both methods can also be used in intramolecular ring closure reactions to form cyclic ketones. Similar, but not identical reaction mechanisms are assumed. The first reaction resembles hydroformylation and requires carbon monoxide insertion and an additional metal acyl alkene insertion step, while in the second reaction the carbon monoxide unit is already present in the substrate. This reaction starts with an oxidative addition to the aldehyde C-H bond, forming an acyl metal hydride, which then undergoes alkene insertion and reductive elimination. 

Red-purple crystals of ehloro-bis 2-(2-oxyphenyl)benzothiazolato oxotcchnctium(V), [TcO(hbl)2Cl]" were obtained by evaporation of a solution of [TcO(sphsal)CI " in dichloromethane/heptane. ITie Hhbt ligand is reported to be formed from H2sphal by an oxidative intramolecular ring closure reaction ... 

Another possibility of meta substitotion is represented by the intramolecular ring closure reaction of suitable substituent introduced into the para-position. This approach (see Sect. 3.6), so far only rarely used in calixarene chemistry, leads to systems with condensed polycyclic arrangement. As an example we can mention the photochemical condensation of styryl-substituted cafixarene to form a compound containing a phenanthrene moiety (Scheme 3.1). 

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