cyclopropanation

Cyclopropanation is a chemical reaction that forms a cyclopropane ring. This is typically achieved by the addition of a carbene or a carbene equivalent to an alkene. The cyclopropane ring is a three-membered carbon ring, and its formation involves the creation of two new carbon-carbon bonds. This reaction is a fundamental transformation in organic chemistry and is widely used in the synthesis of various organic molecules, including pharmaceuticals and natural products.

Several methods exist for performing cyclopropanation. One common approach involves the Simmons-Smith reaction, which utilizes diiodomethane and a zinc-copper couple to generate a zinc carbenoid species. This carbenoid then adds to an alkene to form the cyclopropane. Another important method is the addition of diazo compounds in the presence of transition metal catalysts, such as rhodium or copper complexes. These catalysts promote the decomposition of diazo compounds to form carbenes, which then undergo cyclopropanation with alkenes. Asymmetric cyclopropanation, which leads to the formation of chiral cyclopropane products, can be achieved using chiral catalysts or chiral auxiliaries. The stereochemistry of the alkene often influences the stereochemistry of the resulting cyclopropane. Cyclopropanation reactions are valuable for introducing strain into molecules, which can be exploited for further chemical transformations.