Irradiation cyclophanes

The synthesis of a new benzo[6]furan-containing cyclophane has been achieved by irradiation of the starting diketone 113 via a 6-hydrogen abstraction from the o-alkoxybenzophenone. X-ray analysis shows that the cyclophane has a well-defined rectangular cavity <00TL1393>. 

Similar intramolecular cycloadditions are encountered where an ether linkage has been incorporated into the met a or para linking groups 123. In these cyclizations the better yields were obtained from the para-attached systems. The yields obtained are again dependent on the chain length of the separator and are indicated below the appropriate structures (124)57. Other hetero-atom-substituted cyclophanes (125) can be obtained by irradiation of the divinyl compounds (126)58,59. The use of tin and germanium derivatives... 

The aryl groups of the styryl systems need not be unsubstituted, as has been illustrated before for the cyclizations encountered in the synthesis of naphthalenophanes from 120. Indeed cyclization to afford a cyclobutane derivative where methoxy groups are on the adjacent ring position to the vinyl moieties has also been studied. The irradiation of 138 affords the m-cyclophanes 139 and 14065. Further study has sought to evaluate the steric effect of o-methoxy groups in such molecules66. 

The cyclophane (29) on irradiation with a low-pressure mercury lamp at 20 °C or —190 °C undergoes opening to afford relatively stable solutions of (30 Scheme 6) which was detected by its UV spectrum (76AG(E)442). 

Intramolecular photocyclodimerizations of styrene systems of type 66 have been applied50 for the synthesis of cyclophanes (Scheme 14). The irradiation of compound 66a afforded straight photoproducts 67, subsequently transformed, upon reductive cleavage of the produced four-membered ring, to cyclophane 68. The approach seems successful for longer chains between the styrene units and allows introduction of heteroatoms such as oxygen51, 52 (69) and silicon53 (66b). 

Perhaps the most common tethering is the use of alkyl linked styrenes that result in cyclophanes upon irradiation [24]. Okada et al. have reported several systems that undergo efficient alkene+alkene photocycloaddition (see Sch. 13) [25]. A common explanation for the effectiveness of the cycloaddition between these tethered styryl groups is that 7i-stacking orients the alkenes in close proximity so that the excited state alkene can readily interact with the adjacent ground-state alkene. 

Irradiation of macrocycles having two l,5-dibenzoyl-2,4-dialkoxybenzene moieties with a 350 nm mercury lamp followed by dehydration afforded benzo[l,2-b 5,4-fc ]difuran-containing cyclophanes via a quadruple photocyclization in a one-pot operation as illustrated in the following scheme <02H(57)657>. Facile routes for the synthesis of novel cyclophanes containing both benzo[ 1,2-b 5,4-b ]difuran and naphthalene rings were developed in a similar manner <02JCS(P1)310>. 

In this same vein, the synthesis of 25m and 2621) has been attempted by initial formation of the cyclic sulfides, then extrusion of sulfur by irradiation in the presence of triethylphosphite. In both cases the limited sample size precluded formation of the desired cyclophanes (25 and 26) by this photolytic procedure. Variable temperature H NMR studies have been performed on 27 and 28 27 has a barrier to conformational inversion of 12.5 kcal/mole, while 28 has a corresponding barrier of 10.4 kcal/mole. Phane 28 exhibits a shift of the aromatic protons to higher field as compared to 29 the most dramatic shift is observed for H-3, which absorbs at 7.72 ppm for 28 and at 8.37 ppm for 29. This shift has been explained in terms of an approximately syn orientation of the pyridine rings in 28. 

The first approach has been pioneered by Hopf and coworkers by covalently attaching polyene chains onto a rigid molecular fragment, a [2.2]-paracyclophane. " The paracyclophane scaffold serves as a template to hold the two polyenes in the vicinity for a sequential [2 + 2] photodimerization. The covalent attachment of the polyene chains onto the cyclophane effectively makes the dimerization an intramolecular process (Figure 15). Upon UV-irradiation... 

B) Data Analysis. Irradiation was performed with a high pressure mercury lamp (250W, Ushio Electrics Co.). The two dichroic absorbance components of HNMA and Cyclophane at 393.5tun and 402nm were monitored at room temperature after irradiating the sample over different time intervals with linearly polarized light at 365nm. The reorientation dynamics of these molecular tracers were obtained from the analysis of the time-dependent induction efficiency qft) which is defined as" r (t) = 100. ODx(t) - ODii (t) /ODo (1)... 

It is reported that the bridged Dewar benzene (7) upon irradiation in a low temperature matrix produces a product whose U. V./visible absorption spectra are consistent with the formation of the cyclophane (8). 2 Thus (8) is trapped to... 

Irradiation of the [18]-annulene derivative (142) results in the formation of a complex novel cyclophane in 68% yield. The synthesis of pentalene (143) has been achieved by the irradiation of the dimer (144) in an argon matrix. The process occurs in two steps. 

Timmermans et al. report that diastereoselectivity can be induced in the intramoleuclar meta photocycloaddition of ethenes to the benzene ring as a result of minimisation of steric interactions between substituents on the linking tether of the bichromophore and a methoxy group at the 2-position of the arene unity this type of photoprocess has also been used as a key step in a formal synthesis of crinipellin B (Wender and Dore). New polycyclic cage compounds 43 have been obtained by irradiation of the [3.3,3] (1,3,5) cyclophane 44 (Sakamoto et al.) and Kubo et al. have described the intramolecular [3 + 2] photocycloaddition of bichromophores such as 45 which gives rise to nine- to eleven-membered ring systems 46. 

The cyclophane (163) undergoes cyclization when irradiated in solution in the presence or absence of water and a low yield of the cycloadduct (164) is obtained which itself is also photochemically reactive and undergoes a further... 

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