Dipolar Cycloaddition Lab Report

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1. Introduction to 1,3-dipolar cycloaddition reaction The reaction in which two or more π electron systems combine to form stable cyclic molecules during which sigma bonds are formed between the terminal π electron systems and no fragments are lost are called cycloaddition reaction. A concerted mechanism requires a single transition state and no intermediate, which lies on the reaction path between reactants and adducts. The two important cycloaddition reactions that usually follow concerted mechanism are: (a) Diels-Alder reaction: The addition of conjugated diene to an alkene (usually called as dienophile) to give a six membered ring system are called Diels-Alder reaction or [4+2]-cycloaddition reaction. (b) 1,3-Dipolar cycloaddition:…show more content…
The 1,3-Dipolar cycloaddition constitute a powerful classical synthetic tool for the construction of five membered heterocycles such as isoxazoles, isoxazolines, pyrazoles, pyrazolones, 1,2,4-oxadiazolines etc. and one of the most productive fields in modern organic chemistry1. The concept of 1,3-dipolar cycloaddition was introduced by Huisgen and co-worker after 1960s by publishing a large number of research articles. He defined 1,3-dipole (ylide) as an a-b-c structure with negative and with positive charge distributed over three atoms and has four π electrons. So a five membered ring is formed by the cycloaddition of 1,3-dipole molecule (a three atom entity; a-b-c) and dipolarophile (a two atom entity; d-e) (Scheme-1.

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