Cyclic reaction with nucleophiles

The reactions with nucleophiles include a wide variety such as amines, sulfides (133,135), diazomethane (111), and others. Of particular interest were the reactions of such intermediate iminium salts with 2,3-dimethyl-butadiene to give cyclic products as shown in the reaction of N-bromo-methylpiperidine and N-bromo- and N-chloromethyldiethylamine (134). 

Williams, A., and Ibrahim, I.A. (1981) A mechanism involving cyclic tautomers for the reaction with nucleophiles of the water-soluble peptide coupling reagent l-ethyl-3-(3-dimethyla-minopropyl) carbo-diimide (EDC)./. Am. Chem. Soc. 103, 7090-7095. 

The general process (23) in which mechanism SE2(cyclic) operates may be described in two ways either as an SE2(cyclic) reaction with the substrate RMX and the reagent E(B)N, or as an SE2(cyclic) reaction with the substrate RMX and the reagent EN catalysed by the nucleophile B. Ingold3 has used the former description, and this is perhaps the simplest procedure. 

Several recent publications describe cleavage of 1,3,2-dioxathiolane. S -dioxides (cyclic sulfates) by halide nucleophiles that furnish halohydrines, which can be used as synthetic intermediates, primarily for preparation of corresponding epoxides or for further reactions with nucleophiles (Table 6). Similar reactions with chloride have been studied for 1,3,2-dioxathiolane J-oxides (cyclic sulfites) <1996ACS832>. 

The N-oxides of special position, although their reactions with nucleophilic reagents are similar to the reactions of other imines. These compounds have been studied particularly in connection with attempts to synthesize the cyclic skeleton corrin of vitamin B12. 

Reactions with nucleophiles. Many of these reactions have been carried out with cyclic sulfate 1, available in 90-93% yield from diisopropyl (+ )-tartrate. This sulfate is reduced at pH 4-5 by sodium cyanoborohydride in THF to diisopropyl (R)-malate in 55% (equation II). 

Ring opening of epoxides proceeds smoothly by the reaction with nucleophilic selenium species, whereas the opening of larger cyclic ethers, such as THF, does not proceed under normal conditions. As demonstrated in Scheme 1, ring open-... 

The nitrogen atoms of cyclic amines are readily substituted by reaction with nucleophiles (usually alkyl halides in base), or with Michael acceptors (usually acrylic compounds). A variety of TV-substituted cyclams, e.g., (54), (57), and homologues, has been prepared by reducing substituted dioxo cyclams (53) and (56). TV-Functionalization can be introduced for precursors before cyclization, e.g., (20), (24), (52), and (55), and the azacyclam macrocycles (74)-(79). 

Reactivity (General Topics, Reactions with Electrophiles and Oxidants, Reactions with Nucleophiles and Reducing Agents, Reactions toward Free Radicals, Carbenes, etc., Reactions with Cyclic Transition State, Reactivity of Substituents, Heterocycles as Intermediates in Organic Synthesis). 

Perhaps the most widely exploited cyclic monomer in reactive processing of composite materials via a stepwise reaction is the oxirane or epoxy group (Hodd, 1989). Epoxy resins are principally used to form three-dimensional networks, but linear polymerization is possible. The main linear polyaddition reactions involve catalysed ring-opening in an ionic chain reaction. However, it is appropriate to consider the chemistry of the oxirane group in its reaction with nucleophilic reagents, principally amines, at this point so that the range of possible reactions may be introduced. 

Dithioles with hydroxy and thiol substituents are protonated forms of l,2-dithiole-3-ones (2a) and -3-thiones (2b) respectively, which are regenerated on deprotonation. The reactions with nucleophiles of 3-alkoxy and 3-alkylthio-1,2-dithiolium salts give dealkylation products only in minor amounts. Instead, nucleophilic attack occurs on the ring (Section 3.11.4.2(iv)). A l,2-dithiolium-4-thiolate (98) readily acylates on an amine function to form a l,2-dithiolo-l,2-dithiole (99). This unusual reactivity is explained by the relative preferences for cyclic and acyclic forms of mesoionic forms <91EGP293120>. 

Homoconjugate reactions. In comparison to cyclopropane-1,1-dicarboxylic acid, the cyclic acylal (1) shows pronounced double-bond character in reactions with nucleophiles. Thus it reacts with piperidine in benzene at 20° to give the zwitterion (2) in quantitative yield. The second reaction (II) is an example of the... 

The cyclic anhydrides 583 undergo exothermic reactions with nucleophiles as indicated (Scheme Whether a nucleophile attacks carbonyl carbon or phosphoryl phos-... 

Note that this reaction with nucleophiles is the reverse of the formation of the cyclic sulfonium salt. 

Nishiyama Y, Katoh T, Deguchi K, Morimoto Y, Itoh KJ (1997) Stereoselective synthesis of 2,2,5-trisubstituted tetrahydrofurans via the Lewis acid assisted reaction of cyclic hemiketals with nucleophiles. J Org Chem 62 9339-9341... 

Monomers. Two broad types of monomers can be polymerized anionically vinyl, diene, and carbonyl-type monomers with diftmctionahty provided by one or more double bonds and cyclic (eg, heterocyclic) monomers with difunctionality provided by a ring that can open by reaction with nucleophiles. For vinyl monomers, there must be substituents on the double bond that can stabilize the negative charge that develops in the transition state for monomer addition, as shown in equation 8 ... 

Polycarbophosphazenes possess a backbone of phosphorus, nitrogen, and carbon atoms and can be regarded as derivatives of classical polyphosphazenes (1) in which every third phosphorus atom is replaced by carbon. The first examples of these materials were discovered in 1989 (88). Thermal ROP of a cyclic carbophos-phazene was used to prepare the chlorinated polymeric species (23), which im-dergoes halogen replacement reactions with nucleophiles such as aryloxides and aniline to yield hydrolytically stable poly(aryloxycarbophosphazenes) (24) (Afw = ca 10 , Mn = 10 ) (eq. 23) (88-91). The polymer backbone in these materials was found to be less flexible than in classical polyphosphazenes. For example, the halo-genated polymer (23) possesses a Tg of —21°C compared to a value of —66°C for poly(dichlorophosphazene) (2). 

The ROP of six-membered cyclic carbonates with nucleophilic initiators is a chain reaction in which, besides initiation and propagation reactions, transesterification reactions can also take place (Scheme 32).Intramolecular nucleophile (e.g., alkoxide) attacks on carbonyl carbon atom (backbiting) lead to cyclic oligomers, while intermolecular transesterifica-tion leads to a change of the macromolecule length with the consequence that, at equilibrium, the most probable distribution of the molecular weight is obtained (Scheme 32). 

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