Asymmetric electrophilic fluorocyclization with carbon nucleophiles

Bromination and chlorination of aromatic rings by electrophilic aromatic substitution reactions are easily achieved, but fluorination and iodination are difficult to achieve. Fluorine is so reactive that its reaction with benzene is difficult to control, resulting in poor yields of monofluoroaromatic products. To address this, Selectfluor reagent is used as a fluorine source in which a fluorine atom is bonded to a positively charged nitrogen.

The Friedel–Crafts acylation reactions involve the addition of an acyl group to an aromatic ring. These reactions proceed via electrophilic aromatic substitution by employing an acyl chloride and a Lewis acid catalyst such as aluminum chloride to form aryl ketone.

Friedel–Crafts reactions were developed in 1877 by the French chemist Charles Friedel and the American chemist James Crafts. Friedel–Crafts alkylation refers to the replacement of an aromatic proton with an alkyl group via electrophilic aromatic substitution. A Lewis acid catalyst such as aluminum chloride reacts with an alkyl halide to form a carbocation. The resulting carbocation then reacts with the aromatic ring and undergoes a series of electron rearrangements before giving the final...

Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.

Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.

This lesson explains the definition, classification, and characteristic features of an electrophile that are key features of nucleophilic substitution reactions. An analysis of their charge and orbital picture helps understand their reactivity for seeking electrons. Electrophiles can be classified into positive and neutral species. Other classes include free radicals and polar functional groups.
While a positive electrophile, like a proton, reacts due to its vacant, low-energy 1s orbital, the...