Algar–Flynn–Oyamada reaction explained

The Algar–Flynn–Oyamada reaction is a chemical reaction whereby a chalcone undergoes an oxidative cyclization to form a flavonol.^{[1] [2]}

Reaction mechanism

There are several possible mechanisms to explain this reaction; however, these reaction mechanisms have not been elucidated. What is known is that a two-stage mechanism exists. First, dihydroflavonol is formed, which then subsequently oxidizes to form a flavonol.

Proposed mechanisms involving epoxidation of the alkene have been disproven.^[3]

The probable mechanisms are thus two possibilities:

• The phenoxide attacks the enone at the beta position, and the alkene directly attacks hydrogen peroxide from the alpha position, forming the dihydroflavonol.
• The phenoxide attacks the enone at the beta position, closing the six-membered ring and forming an enolate intermediate. The enolate then attacks hydrogen peroxide, forming the dihydroflavonol.

See also

• Allan–Robinson reaction
• Auwers synthesis

Notes and References

1. none. Algar, J. . Flynn, J. P. . Proceedings of the Royal Irish Academy. 1934. 42B. 1.
2. Oyamada, B.. 10.1246/bcsj.10.182. A New General Method for the Synthesis of the Derivatives of Flavonol. 1935. Bulletin of the Chemical Society of Japan. 10. 5. 182–186. free.
3. Gormley. T.R.. O'Sullivan. W.I.. Flavanoid epoxides—XIII. Tetrahedron. 29. 2. 1973. 369–373. 0040-4020. 10.1016/S0040-4020(01)93304-6. 10197/6996. free.