Brandi-Guarna reaction

What is Brandi-Guarna reaction?

The Brandi et al. were likely the first to report the Brandi-Guarna reaction in 1986. This chemical process encompasses a range of reactions used to create tetrahydropyridone derivatives. It begins with the 1,3-dipolar cycloaddition of nitrones and alkylidenecyclopropanes, yielding a mixture of isoxazolidine regioisomers with spiro-fused cyclopropane rings positioned on C4 and C5. Then, the resulting 1,3-dipolar cycloadducts undergo thermolysis through a unique homolytic cleavage of the weak nitrogen-oxygen bond, followed by the opening of the adjacent cyclopropane ring and closure of the diradical, ultimately producing tetrahydropyridones. Cyclic nitrones yield N-bridgehead bicyclic ketones.

Brandi-Guarna reaction - general reaction scheme - Brandi reaction
Brandi-Guarna reaction
  • R, R’ = alkyl, aryl (see list of acronym)

This reaction is also known as the Brandi reaction. Additionally, similar reactions involving the 1,3-dipolar cycloaddition of alkylidenecyclopropanes and nitrile oxides, followed by ring enlargement to form aza-heterocycles, are also referred to as the Brandi reaction.