Cyclopropanation

It is an important process in modern chemistry as many useful compounds bear this motif; for example pyrethroid insecticides and a number of quinolone antibiotics (ciprofloxacin, sparfloxacin, etc.).

The first step involves a 1,3-dipolar cycloaddition to form a pyrazoline which then undergoes denitrogenation, either photochemically or by thermal decomposition, to give cyclopropane.

The thermal route, which often uses KOH and platinum as catalysts, is also known as the Kishner cyclopropane synthesis after the Russian chemist Nikolai Kischner[7][8] and can also be performed using hydrazine and α,β-unsaturated carbonyl compounds.

[10][11] In terms of green chemistry this method is superior to other carbene based cyclopropanations; as it does not involve metals or halogenated reagents, and produces only N2 as a by-product.

Methyl phenyldiazoacetate and many related diazo derivatives are precursors to donor-acceptor carbenes, which can be used for cyclopropanation or to insert into C-H bonds of organic substrates.

[16] Cyclopropanes can be generated using a sulphur ylide in the Johnson–Corey–Chaykovsky reaction,[17] however this process is largely limited to use on electron-poor olefines, particularly α,β-unsaturated carbonyl compounds.

The precursor to the hormone ethylene, 1-aminocyclopropane-1-carboxylic acid, is derived directly from SMM via intramolecular nucleophilic displacement of the SMe2 group subsequent to condensation with pyridoxal phosphate.