Overview

Cycloadditions Background-

I. Cycloadditions are one of the three main pericyclic reactions that occur in a concerted process. The transition state assumes a cyclic rearrangement of electrons. This process often features two or more unsaturated compounds that combine and form a cyclic adduct. 

II. For example, the Diels-Alder reaction undergoes a [4+2] cycloaddition as shown. As we can see, this simple Diels-Alder reaction produces a monosaturated cyclic adduct when the diene and dienophile react in the presence of heat. This named reaction was discovered by German chemists Otto Diels and Kurt Alder who won the Nobel Prize in Chemistry in 1950 for this reaction

1. In this example, the Diels-Alder reaction is catalyzed by the enzyme Spirotetronate cyclase to create a new cyclic adduct, Abyssomicin C Precursor. This molecule inhibits p-aminobenzoate (PABA) formation, a crucial step in bacterial folate biosynthesis. 

• We observe here an intermolecular [4+2] cycloaddition occuring on this substrate when coordinated to Spirotetronate cyclase AbyU. 

     2. Another case of a cycloadditon taking place is a [2+2] cycloaddition during the Wittig Reaction when the ylide and a ketone OR aldehyde interact (Shown below). The Wittig reaction is critical in turning aldehydes or ketones into alkenes; very useful in organic synthesis.