Synthesis, Photochemistry, and Photophysics of Butadiene Derivatives: Influence of the Methyl Group on the Molecular Structure and Photoinduced Behavior

Abstract

Novel butadiene derivatives display diverse photochemistry and photophysics. Excitation of 2-methyl-1-(o-vinylphenyl)-4-phenylbutadiene leads to the dihydronaphthalene derivative, whereas photolysis of the corresponding model o-methyl analogue results in the formation of the naphthalene-like derivative, deviating from the nonmethylated analogue of the prior starting compound and producing benzobi- and -tricyclic compounds. The effect of the methyl substituents is even more dramatic in the case of the dibutadienes. The parent unsubstituted compound undergoes photoinduced intramolecular cycloaddition giving benzobicyclo[3.2.1]octadiene, whereas the photochemical reaction of the corresponding dimethylated derivative shows only geometrical isomerization due to the steric effect of the substituents. Methyl groups on the butadiene backbones reduce the extent of conjugation, causing a blue-shift of the characteristic absorption band. The fluorescence efficiency is dramatically decreased, as a consequence of nonplanarity and reduced rigidity of the molecules due to the crowding by the methyl and phenyl groups together. Four molecules of very similar structures show dramatically different photoinduced behavior, revealing how changes of the nature and position of the substituents are valuable in understanding the photophysics and photochemistry of these types of compounds.

A simple and easy to perform synthetic route to functionalized thienyl bicyclo[3.2.1]octadienes

“…The bicyclo [3.2.1]octane skeleton has become the subject of intensive research in recent years [1][2][3]. Its presence in numerous biologically active natural compounds ( Figure 1) [4][5][6][7], their strenuous isolation procedures from plants, as well as their complicated multistage synthesis due to the complexity of their structure, encouraged us to develop a simple one-step synthetic procedure based on a photochemical methodology [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. By using a simple photochemical procedure, it was possible to obtain a whole library of novel bicyclo[3.2.1]octadiene derivatives, available for further functionalization, which could enable the easier investigation of the relationship between structure and biological activity.…”

Antiinflammatory and Antiproliferative Activity of Naphthoxazole, Fused Hetero-benzoxazole and Bridged Benzobicyclic Photoproducts

“…[21] Bicyclo[3.2.l]-skeleton can be constructed using different synthetic pathways, one of which is the photochemical cycloaddition approach that has been developed by our group in batch and flow photochemical reactor. [22][23][24][25][26][27][28][29][30][31][32][33][34] Guided by all above mentioned compounds, we have selected 32 compounds from both types of photoproducts and investigated their biological activity in proliferation and inflammation based assays. Effect of compounds on proliferation of several cancer cell lines was determined by measuring cell metabolic activity through time.…”

Photochemical Approach to New Polycyclic Substrates Suitable for Further Photocatalytic Functionalization

“…1−3 Unsubstituted starting compounds 1a and 2a, upon irradiation at 350 nm, give as the main products of intramolecular cycloaddition benzobicyclo[3.2.1]octadiene structures endo-3 and endo,trans-4, respectively. 1,2 The bicyclo[3.2.1]octane skeleton, saturated analogue of the bicyclo[3.2.1]octadiene, is found in numerous biologically important active natural products. 4−20 Moreover, benzobicyclo[3.2.1]octadiene skeleton is also an important fragment in biologically active compounds or it can be used as a suitable substrate for further transformations on the isolated double bond, easily derivatized to new compounds with various functionalities.…”

“…21−27 As a part of our increasing interest in the photochemistry of conjugated butadiene systems and to explore the effect of substituents on the butadiene units on the photochemical reactions, studies are expanded to methyl-and chloro-butadiene derivatives 1b−d and 2b−d. 2,3 Methyl group effects sterically to photochemical reactions, causing diverse photoinduced behaviour and formation of completely different photoproducts. 2 Monosubstituted methyl derivative 1b upon irradiation gives dihydronaphtalene derivative 5 (Figure 2), while disubstituted methyl derivative 2b shows only geometric isomerization.…”

“…2,3 Methyl group effects sterically to photochemical reactions, causing diverse photoinduced behaviour and formation of completely different photoproducts. 2 Monosubstituted methyl derivative 1b upon irradiation gives dihydronaphtalene derivative 5 (Figure 2), while disubstituted methyl derivative 2b shows only geometric isomerization. Introduction of the chlorine atom to butadiene unit can lead the reaction course to various direction, under its steric and electronic effects.…”