Harnessing the Power of the De Mayo Reaction: Unveiling a Photochemical and Photocatalytic Masked [2+2] Methodology for Organic Synthesis

Abstract

In 1962, Paul J. de Mayo initially described the photochemical reaction involving 1,3‐diketones and double bonds, resulting in the formation of 1,5‐diketones. Since then, this reaction has been extensively utilized for the synthesis of a wide range of fascinating natural products. Over time, this synthetic methodology has been applied to various carbonyl systems, including locked enol‐tautomers of diketones, β‐keto esters, and β‐enaminones. Additionally, it has found application in other unsaturated systems such as allenes and alkynes. In this review article, we provide a comprehensive overview of the classical de Mayo reaction, highlighting its scope and potential. Furthermore, we focus on recent advances achieved through photocatalytic conditions. Special emphasis is placed on the regioselectivity of the process and the underlying reaction mechanism, particularly within the context of photocatalysis.

Charge-recombinative triplet sensitization of alkenes for DeMayo-type [2 + 2] cycloaddition

“…In the DeMayo-type [2 + 2] cycloaddition reaction, substrate triplet sensitization is a critical step. 36,40–42,44 Thus, our investigation emphasized elucidating how indole-based polycyclic organoPCs facilitate photosensitization that leads to the generation of the substrate triplet state.…”

“…Subsequently, our focus shifted toward understanding the photocatalytic process mechanism, particularly the origin of the superior reactivity of A and H. In the DeMayo-type [2 + 2] cycloaddition reaction, substrate triplet sensitization is a critical step. 36,40–42,44 Thus, our investigation emphasized elucidating how indole-based polycyclic organoPCs facilitate photosensitization that leads to the generation of the substrate triplet state.…”

“…1d). 32,33 To investigate this uncommon CRTS mechanism, we utilized an indole-based polycyclic organoPC series, 34,35 developed in our laboratory, for a DeMayo-type [2 + 2] cycloaddition 36–44 between methyl-2-(quinolin-2-yl)acetate ( 1 ) and various styrene derivatives. Detailed studies involving photophysical and electrochemical measurements and computational analyses provide insights into this unique CRTS pathway.…”

TEMPO-Mediated Interrupted 6π-Photocyclization of ortho-Biaryl-Appended 1,3-Dicarbonyl Compounds toward 10-Phenanthrenols

“…The reaction starts with the direct irradiation of the mixture of keto - 1a and enol - 1a isomers with violet light (λ = 390–395 nm), the isomers absorb light energy and are immediately excited to its singlet excited state followed by ISC to its triplet excited state 3 1a *. The triple excited state 1a undergoes classical 6π electrocyclization, which produces transients 1,4-diradical A and B similar to the de Mayo reaction, and then trapped by tandem TEMPO-mediated direct HAT , or Cope-like elimination by losing TEMPOH to give the desired product 2a .…”

Photoinduced Generation of Active Intermediates from Unmodified 1,3‐Dicarbonyl Compounds for Organic Transformations

“…The photochemical reaction of β-diketones and double bonds under UV irradiation is referred to as the de Mayo reaction. [46] In 1962, Paul Jose de Mayo reported that the enol form of 1,3diketones could undergo a [2 + 2] cycloaddition reaction with alkenes under UV irradiation, yielding a cyclobutanol intermediate. This intermediate generates 1,5-diketones after ringopening.…”