Nucleophilic assistance intramolecular

Intramolecular nucleophilic assistance is another distinct possibility for providing activation, and can be realized by coordination of the metal center by a heteroatom (O, N, etc.) within the ligand which transiently forms a chelate-like attachment to the metal. Such a mode of activation was supposed to account for the ease of reaction of vinyl triflates with (zp-isomers of alkenyl-stannanes bearing OH groups in the proximity of the reaction center (71).2 5... 

Enamines are readily available ketone derivatives." Exposure of these compounds to certain transition metal salts has been shown to produce a-oxygenated imines which are rapidly hydrolyzed to their ketone counterparts. Thus, for example, morpholino enamines, prepared in situ, are a-acetoxylated on treatment with thallium triacetate. The process is thought to involve either direct nucleophilic extraction of an acetate unit or the intermediacy of an organothallium species which subsequendy undergoes anchimerically assisted intramolecular acetoxy migration to generate the a-acetoxyimine (Scheme IS). 

The electrophilic cleavage of an alkyl-tin bond can be assisted by a suitably positioned intramolecular ligating group. Thus in 5-3, the ease of the cleavage of the methyl-tin bond is ascribed to nucleophilic assistance by the sulphoxide group.38... 

The difference between these two methods of expressing the magnitude of anchimeric assistance is that the ratios kjk or kjk involve a comparison of two different types of processes an intramolecular displacement, which involves a specific neighboring group as nucleophile (fc ) and an inter-molecular process, which involves the solvent as nucleophile (fcj or one that occurs without nucleophilic assistance (fc ). On the other hand, the effective molarity involves a comparison of two analogous processes that differ only in that one is intramolecular and the other intermolecular. " ... 

Aryl thioethers s. Thioethers, ar. Arylthiomethylation 26,844 Aryl tridiloromethyl carbinols -, reactions with nucleophiles, review 22, 629 suppl. 26 Arynes s. Benzyne..., Hetarynes Ascaiite 11,963 suppl. 28 Asscher-Yofsi reaction 21,642 Assistance, intramolecular s. Neighboring group participation... 

This chapter has taken the reader through a number of microwave-assisted methodologies to prepare and further functionalize 2-pyridone containing heterocycles. A survey of inter-, intramolecular-, and pericyclic reactions together with electrophilic, nucleophilic and transition metal mediated methodologies has been exemplified. Still, a number of methods remain to be advanced into microwave-assisted organic synthesis and we hope that the smorgasbord of reactions presented in this chapter will inspire to more successful research in this area. 

Another synthesis of diazepines (tricyclic) was carried out by reaction of an amino chloropyridine 258 and anthranilic acid [163]. First, a nucleophilic substitution occurred (Scheme 95) followed by an intramolecular amidation on compound 259 by microwave irradiation to give structure 260. The reaction was carried out at 100 °C for more than 2 h, a remarkably long time for a microwave-assisted reaction. 

This system was described in one report and has been synthesized by a copper-assisted cycloisomerization of alkynyl imines. The authors proposed the following mechanism at first, 372 could undergo a base-induced propargyl-allenyl isomerization to form 373 next, coordination of copper to the terminal double bond of the allene (intermediate 374) would make it subjected to intramolecular nucleophilic attack to produce a zwitterion 375. The latter would isomerize into the more stable zwitterionic intermediate 376, which would be transformed to the thiazole 377 (Scheme 55) <2001JA2074>. 

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