Nucleophilic ring-opening reactions

The regioselectivity of such nucleophilic ring-opening reactions can sometimes be... 

The progress on S-C bond activation, which covers the reduction of a C-S bond to a C-H bond, cross coupling reaction of sulfides with main group organometaUic nucleophiles, ring opening reactions of thietanes and thiiranes, and desulfurization of thiols, sulfides, and thiophenes has already been reviewed elsewhere [6-10], and... 

The primary type of epoxide reaction remains the nucleophilic ring-opening reaction. Research on the development of novel catalysts or catalytic systems for epoxide opening continues to be a highly active area of study. 

Me o-epoxides, nucleophilic ring-opening reactions by aryllithium/(—)-sparteine (11) have been realized by Alexakis and coworkers with very good differentiation between the enantiotopic positions . Eliminative desymmetrization reactions of me o-oxacycles such as 144 or 147, which are triggered by an enantiotopos-differentiating deprotonation... 

Wordy Over the past few years, we have encountered numerous examples of water as the perfect solvent. We observed this first in osmium-catalyzed dihydroxylation reactions and also in nucleophilic ring-opening reactions of epoxides. We also observed this in cycloaddition reactions and in most oxime ether, hydrazone, and aromatic heterocycle condensation processes.Finally, we observed it in formation reactions of an amide from a primary amine and an acid chloride using aqueous Schotten-Baumann conditions. ... 

The polymerization of an unsymmetric epoxide such as propylene oxide involves the possibility of two different sites (at carbons 1 and 2 or a and (3) on the epoxide ring for the nucleophilic ring-opening reaction. Two different propagating species are then possible ... 

Available data on the reactivity of these systems were discussed in CHEC-II(1996) <1996CHEC-II(7)737> and little has been published since, the most notable report being of nucleophilic ring-opening reactions to form 4-aminocinno-line-3-carboxamides (Equation 125) <1997PHA838>. 

Nucleophilic Ring-Opening Reactions of 1 General Procedure 31... 

In this section we discuss the opening of the thiophene ring by Grignard reagents. Nucleophilic ring-opening reactions of cyano- and nitro-thiophenes are relegated to the appropriate sections (3.14.3.3 and 3.14.3.5). 

In these nucleophilic ring-opening reactions the amine attacks the less sterically hindered car-... 

Epoxides are sensitive to nucleophilic ring-opening reactions. Phenoxide ion attacks the less hindered carbon to yield l-phenoxy-2-propanol. 

Although some examples of electrophilic substitution are known, the chemistry of these series is dominated by nucleophilic ring-opening reactions, sometimes followed by ring-closure to give new heterocycles. For instance, aminolysis of 9.1, 9.2, and 9.3 leads to pyridine 5.1 and pyridones 5.22 and 5.23. 

Nucleophilic substitution in the azine ring is a normal reaction. The fused oxazole ring, however, is susceptible to nucleophilic ring opening reactions, especially in oxazolium salts and dihydro derivatives. When fused to pyrimidine, substituents in the pyrimidine ring may promote a Dimroth rearrangement of the latter. 

The thiadiazoles are 7r-electron deficient. This enhances the reactivity of substituents in the azine ring, and this is most pronounced in the orthoquinonoid systems. But the electron deficiencies of these systems make them vulnerable for nucleophilic ring opening reactions. Sometimes the preferred reaction pathway may be difficult to predict. The nucleophilic ring opening reactions are treated in a separate section. 

Employing an excess of the organometallic reagent (2 equiv) at 100 °C resulted in the formation of ketopyrrole (S)-79 in 87% yield. Obviously, compound (S)-79 is produced by successive N-acylation, t>-directed metallation and N,C-acy migration. Nucleophilic ring-opening reaction of the lactone (S)-77 with A -methylpyrrole lithiated in 2-position (with Bu Li/TMEDA) proceeded smoothly furnishing the ketone (S)-79 in 62% yield. 

Potassium hydrogen fluoride or sodium hydrogen fluoride may serve as a fluoride ion source for the nucleophilic ring-opening reaction of epoxides. Attack of fluoride occurs predominantly at the less-hindered, i.e. least-substituted, site in the epoxide, as discussed in the following examples. 

The reactions of fused-ring aziridines are largely limited to ring-opening reactions. An excellent review of nucleophilic ring-opening reactions has appeared <2004T2701> that contains both fused cyclic systems and acyclic... 

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