Myers-Saito cyclization

What is Myers-Saito cyclization?

In 1989, Myers et al. and Saito et al. independently reported the thermal intramolecular cyclization of eneyne-allene, which generates a σ,π-biradical intermediate through the bonding of C2 and C7. This reaction is commonly known as the Myers-Saito cyclization, or the Myers-Saito enyne-allene cycloaromatization reaction.

Myers-Saito cyclization - general reaction scheme - Myers-Saito enyne-allene cycloaromatization reaction
Myers-Saito cyclization

Unlike the Bergman cyclization, this reaction occurs smoothly even at low temperatures, owing to its cyclic electron delocalization. The partially conjugated σ,π-biradical in this reaction is less reactive than the σ,σ-biradical in the Bergman cyclization.

The reaction can also be initiated by light, acid, or base, but the rate is sensitive to the substituents on the alkyne and allene moieties. When an aryl or a sterically bulky group (such as t-Bu or SiMe3) replaces the hydrogen at the alkyne terminus, the C2-C7 cyclization is switched to the Schmittel cyclization by forming a bond between C2 and C6. This reaction is valuable in constructing polycyclic aromatic ring systems and developing potential anticancer drugs, such as neocarzinostatin.