Photochemical Syntheses: 9. The Conversion of Dibenzoylmethane to Tribenzoylethane

Abstract

Irradiation of dibenzoylmethane in benzene gives tribenzoylethane. In more concentrated solution a solid dimer (11) separates which, on solution, is converted by dealdolization into a n isomer. This isomer (I, R = H) on irradiation, gives tribenzoylethane in a photolytic reaction which has been shown t o have some generality. The overall conversion of dibenzoylmethane t o tribenzoylethane therefore involves two photochemical and one chemical reactions.Some time ago, as part of our studies on photochemical cyclo-addition, we reported the reaction between acetylacetone and a number of alkenes and cycloalkenes (1). The main products derived from the process are indicated below.T o ascertain whether the process was general for all enolized P-diketones, we studied the reaction between dibenzoylmethane and cyclohexene. This diketone is largely enolized in hydrocarbon solvents and the reaction could be conveniently followed by observing the formation of the non-enolized benzoyl grouping in the carbonyl region.The products proved difficult to crystallize and the first substance obtained in crystalline form, from a study of its spectra, evidently did not contain a cyclohexyl residue. This conclusion was confirmed when it was found that the yield was greatly increased (to 37%) by irradiation of dibenzoylmethane in benzene solution.*The substance showed only benzoyl carbonyl in the infrared spectrum, and the ultraviolet absorption was typical of acetophenones. The nuclear nlagnetic resonance (n.m.r.) spectrunl showed the presence of only three protons other than aromatic hydrogen. These were a doublet (two protons) a t T 6.23 and a triplet (one hydrogen) a t T 3.85. These protons were coupled with J = 7 c.p.s. The two protons of the doublet were evidently identical. This required the part structure -CH2-CH / \.Alkaline hydrolysis of the substance under mild condition gave diphenacyl and benzoic acid (1 mole) as the only isolable products. The substance was therefore identified as tribenzoylethane. The remarkably low-field position of the methine proton is noteworthy.The illode of genesis of the tribenzoylethane was not immediately obvious, but since two n~olecules of dibenzoylmethane, a t least, were required to participate in its formation the possibility of dimerization a t some stage appeared reasonable. Accordingly, the irradiation was performed with a higher concentration of dibenzoylmethane.Under these conditions the reaction proceeded differently. Although the infrared spectrum of the solution appeared to be showing the expected changes, a white crystalline solid separated during the irradiation. This material was separated by filtration and * W e are indebted to Mr. R. W. Yifi for this observation.

Leptosperols A and B, Two Cinnamoylphloroglucinol–Sesquiterpenoid Hybrids from Leptospermum scoparium: Structural Elucidation and Biomimetic Synthesis

“…Previous studies revealed that the De Mayo reaction could occur spontaneously under light mediated conditions (UV and visible light). 9,17 However, it remains to be an interesting question whether this step is enzyme-or nonenzyme-catalyzed in the plant. Compounds 1 and 2 were evaluated for their antiinflammatory effects in vivo.…”

“…Subsequently, a retro-aldol reaction of the formed intermediates i or ii could lead to C8′–C9′ cleavage and produce compounds 1 and 2 . Notably, the intermediates i and ii are unstable due to the presence of the β-hydroxyketone moiety that could induce a retro-aldol process. , Thus, 1 and 2 were proposed to be formed by De Mayo reaction.…”

“…Additionally, a synthetic byproduct was identified (Figure S9), but it was not found in the crude extract of the plant. Previous studies revealed that the De Mayo reaction could occur spontaneously under light mediated conditions (UV and visible light). , However, it remains to be an interesting question whether this step is enzyme- or nonenzyme-catalyzed in the plant.…”

“…Compounds (+)-1 and (−)-1 were a pair of enantiomers. Interestingly, these compounds represent the first example of phloroglucinol derivatives biogenetically constructed by a De Mayo reaction ([2 + 2] cycloaddition followed by retro-aldol condensation), 9 resulting in a sesquiterpenoid unit "inserted" into the cinnamoylphloroglucinol moiety with formation of two new bonds and C8′−C9′ bond cleavage (Figure 1). To provide experimental support for the proposed biosynthetic pathway, the biomimetic synthesis of 2 was achieved using a visible light mediated De Mayo reaction approach.…”

Unsaturated polyester resins with different allyl ethers as crosslinking built-in monomers

“…The above-mentioned photoinitiators undergo a rapid ␣-cleavage (Norrish type I) from their excited triplet state. 19,20 The subsequent photochemical transformation of the resulting radicals pair, however, is quite different. The 1,1-dimethoxybenzyl radical from Irgacure 651 undergoes a secondary fragmentation reaction to yield the inactive methyl benzoate and the active methyl radical (Scheme 3).…”