Photochemical Generation of Cyclophanes from 1,3,5‐Trisubstituted Benzenes with Chalcone Chromophores

Abstract

(E,E,E)-1,3,5-Tricinnamoylbenzene (7a) photodimerizes in solution to the [4.4.4](1,3,5)cyclophane 8a. The process consists of three consecutive steps in which cisoid enone conformations of 7a react in regio-and stereoselective anti-headto-head cycloadditions. (E,E,E)-1,3,5-Tris(3-oxo-3-phenylpropenyl)benzene (13a), an isomer of 7 with reversed enone units, shows a single [2π+2π] cycloaddition of the same type. Due to steric reasons, it is afterwards not capable of intramolecular processes and oligomerizes by intermolecular photo-

Photochemical transformations of chalcone-podands into cyclobutane-containing benzocrown ethers

“…The chemical shifts of these protons are very close, and their identification from usual 1 H NMR spectra is difficult. The unambiguous assignment of 1 H and 13 C signals was performed using 2D [1][2][3][4][5][6][7][8][9][10][11][12][13] In the 13 C NMR spectra, the signals for the olefinic carbon atoms differ significantly in the chemical shifts: δ C α ≈ 122 and δ C β ≈ 139, which makes it possible to identify the corresponding protons by the 2D HSQC data (see Table 1). This assignment is also confirmed by the results of 2D HMBC experiments in which the cross peaks between the nuclei pairs H(6)-C(β) and H(β)-C(2) are observed.…”

“…In symmetric isomers 2 and 4, the H(β,β´) protons are identified by the cross peaks with the C(2) and C (6) carbon atoms in the HMBC spectrum, and the H(α,α´) protons are identified by the cross peaks with the ipso C atom of the phenyl substituent (the enumeration of atoms is given in Experimental).…”

“…At the same time, conformational transitions of chalcones can affect, to a considerable extent, the reactivity of the CH=CH bonds and stereoisomerism of the PCA products. 6 As a rule, the photoinduced dimerization reactions of cinnamic acid derivatives in solutions occur with low stereo and regioselectivity and afford a mixture of cyclobutane containing stereoisomers including those with the α , ε truxillic and β , γ truxinic structures. 4,5 However, on going to macromolecules (crown ethers, podands) capable of pre organization, the regio and stereoselec tivity of the PCA processes were considerably enhanced in some cases.…”

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…Meier and co-workers studied the photochemistry of 1,3,5-tricinnamoylbenzene 230 , a trifold chalcone (Figure ). − Remarkably, they observed upon irradiation at λ > 290 nm in concentrated CH 2 Cl 2 solution ( c = 0.14 M) the formation of a dimer, which contained three cyclobutane rings and exhibited a C 3 symmetry axis. The [2 + 2] photodimerization of 230 was also studied in the crystalline state.…”

Mechanistic and Exploratory Investigations into the Synthesis of 1,3,5-Triaroylbenzenes from 1-Aryl-2-propyn-1-ones and 1,3,5-Triacetylbenzene from 4-Methoxy-3-buten-2-one by Cyclotrimerization in Hot Water in the Absence of Added Acid or Base

“…In view of the usefulness of 5 for the synthesis of cyanine dyes, functional dendrimers, , phenolic molecular glasses . cyclophanes, and several ligands for transition metals, − its synthesis by condensation of the sodium salt of acetoacetaldehyde in the presence of acetic acid in 30–38% yield was documented in 1947 in Organic Syntheses , a publication of reliable synthetic procedures for fundamental organic compounds . More recently, another procedure treating 4-methoxy-3-buten-2-one ( 4 ) in aqueous ethanol with acetic acid as a catalyst giving 5 in 61–64% yield at 77 °C for 48 h was described again in Organic Syntheses.…”