Cyclization reactions intermolecular

These results made it possible to arrive at a sufficiently well-grounded conclusion that the effect of raised heat resistance caused by the formation of intermolecular chemical bonds is not very significant, and that the usually observed considerable increase of heat resistance of PAN fibres as a result of a crosslinkage with bifunctional compounds, is caused not by the formation of intermolecular chemical bonds, as it has usually been thought45, 46, but by cyclization reactions of the nitrile groups with the formation of naphthyridine cycles47. ... 

Nuclear halogenoquinoxalines undergo a wide variety of cyclization reactions, both intra- and intermolecular. The following examples illustrate a selection of these. 

The high-dilution and template methods are frequently used in the synthesis of cyclic compounds with the aim of increasing the yield. The former method is carried out at substrate concentrations lower than 1 mM [18-20]. This reaction condition decreases the contact of the substrate molecules in the solution. The linear intermediate produced prefers the intramolecular cyclization reaction rather than the intermolecular reaction. Therefore, this reaction condition is useful for the intramolecular reaction, method B (Fig. 2). 

The stability of a trivial assembly is simply determined by the thermodynamic properties of the discrete intermolecular binding interactions involved. Cooperative assembly processes involve an intramolecular cyclization, and this leads to an enhanced thermodynamic stability compared with the trivial analogs. The increase in stability is quantified by the parameter EM, the effective molarity of the intramolecular process, as first introduced in the study of intramolecular covalent cyclization reactions (6,7). EM is defined as the ratio of the binding constant of the intramolecular interaction to the binding constant of the corresponding intermolecular interaction (Scheme 2). The former can be determined by measuring the stability of the self-assembled structure, and the latter value is determined using simple monofunctional reference compounds. 

The structure of the reagent, the mechanism of epoxide opening, deoxygenations, dimerizations and intermolecular additions will be discussed first before covering the preparatively much more important cyclization reactions [36]. 

Palladium-catalyzed cyclization reactions with aryl halides have been used to synthesize pyrazole derivatives. V-Aryl-lV-(c>-bromobenzyl)hydrazines 26 participated in a palladium-catalyzed intramolecular amination reaction to give 2-aryl-2W-indazoles 27 . Palladium-catalyzed cascade intermolecular queuing-cyclocondensation reaction of o-iodophenol (28) with dimethylallene and aryl hydrazines provided pyrazolyl chromanones 29 <00TL7129>. A novel one-pot synthesis of 3,5-disubstituted-2-pyrazolines 32 has been achieved with an unexpected coupling-isomerization sequence of haloarene 30, propargyl alcohol 31, and methylhydrazine <00ACIE1253>. 

Enyne metathesis is unique and interesting in synthetic organic chemistry. Since it is difficult to control intermolecular enyne metathesis, this reaction is used as intramolecular enyne metathesis. There are two types of enyne metathesis one is caused by [2+2] cycloaddition of a multiple bond and transition metal carbene complex, and the other is an oxidative cyclization reaction caused by low-valent transition metals. In these cases, the alkyli-dene part migrates from alkene to alkyne carbon. Thus, this reaction is called an alkylidene migration reaction or a skeletal reorganization reaction. Many cyclized products having a diene moiety were obtained using intramolecular enyne metathesis. Very recently, intermolecular enyne metathesis has been developed between alkyne and ethylene as novel diene synthesis. 

Dienes and polyenes can undergo a variety of intermolecular cyclization reactions, the exact nature of which is dependent on the number of double bonds, the relative positions of these bonds with respect to each other, the preferred conformation of the diene or polyene system and the reaction partner. 

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