Enoldiazo compounds are one of the most versatile reagents for cycloaddition reactions in highly efficient constructions of various carbocycles and heterocycles. They have enormous flexibility in their chemical reactions for cycloaddition reactions of metal carbene intermediates. Applications of [3+3]-, [3+2]-, and [3+1]-cycloaddition reactions for highly selective asymmetric synthesis include dihydrooxazines, pyrazolidinones, quinolizidines, tetrahydropyridazines, cyclopentane amino acids, cyclobutenes and azacyclobutenes. Enoldiazoacetates and enoldiazoacetamides are stable at room temperature and below for weeks or months, yet they undergo thermal dinitrogen extrusion at temperatures as low as 50°C to quantitatively form donor-acceptor cyclopropenes that are precursors to the same metalloenolcarbenes that are formed from the corresponding enoldiazo compounds. These donor-acceptor cyclopropenes are themselves highly reactive dipolarophiles or dienophiles that form bi- or tricyclic structures which are subject to further transformations.
