Photoinduced Reactions ofpara-Quinones with Bicyclopropylidene Leading to Diverse Polycyclic Compounds with Spirocyclopropanes

Abstract

Photoinduced reactions of bicyclopropylidene (BCP) with para-quinones (p-quinones) including benzoquinones, naphthoquinones, and anthraquinones were found to proceed via different cycloaddition pathways and lead to diverse polycyclic products bearing spiropropyl moiety. Photocycloaddition of BCP with benzoquinones gave spirooxetanes as the primary products, which upon irradiation were able to rearrange into the spiro[4.5]deca-6,9-diene-2,8-diones as secondary photoproducts. Chemoselectivity of the photocycloaddition of BCP with naphthoquinones relies largely on the substitution groups linked to the C═C in between the two carbonyl groups to give different types of products. Photoreaction of BCP with 9,10-anthraquinone gave not only the spirooxetane product, but also a novel spiro[indan-1,1'-phthalan]-3'-one product whose formation might be initiated by a transannular attack of the C4 cyclopropyl radical to the para-carbonyl group. Mechanisms involved in the formation of diverse primary or secondary products in the photoreactions of BCP with p-quinones were proposed. Some of the photoreactions also hold potentials as useful synthetic protocols for important spiropolycyclic compounds such as sesquiterpenes.

Anthryl‐1,2,4‐oxadiazole‐Substituted Calix[4]arenes as Highly Selective Fluorescent Chemodosimeters for Fe3+

“…The structural identification of anthraquinone 14 was straightforward from its highly symmetrical 1 Ha nd 13 CNMR spectra and comparison with ar eport in the literature. [16] However,t he structurala ssignmentso fc ompounds 13 and 15 were nontrivial based on their spectral data alone. To our delight, products 13, 14,a nd 15 grew nice single crystals when they were recrystallized from am ixture of CH 2 Cl 2 /THF ( Figure 6).…”

“…All these results imply that Fe 3 + can first oxidizet he 9-anthryl motif of 4 into 9-aryl-oxanthrone 13 as an intermediate. Further oxidation of intermediate 13 led to anthraquinone 14 [16] and retro Friedel-Crafts rearranged 15 in 24 and 14 % yield, respectively.N otably,t he 1,2,4-oxadiazole group of intermediate 13 was rearranged to a2 -imidazolylg roup in 15; moreover,t he p-tert-butylphenyl ether underwent ar etro Friedel-Crafts alkylation to form a p-Cl-phenyl ether,p resumably promoted by excess perchlorate ions. The resultso bserved here are reminiscento ft he mechanism reported by Fujita and Fukuzumi [17a] in which 9-alkylanthracenes underwent electrontransfer oxidation with Fe 3 + to give the corresponding radical cations of 9-alkylanthracenes.…”

Diastereoselective Photocycloaddition Reaction of Vinyl Ether Tethered to 1,4‐Naphthoquinone

“…As briefly stated in the Introduction section, the photoreaction of naphthoquinone with olefin is initiated in its excited triplet state via a rapid ISC from the excited singlet state of naphthoquinone. The phosphorescence spectra of ( R )‐ 1 and menadione (as a reference) were recorded in dichloromethane matrix at 77 K (Figure ), affording the triplet energies of 240 and 241 kJ mol −1 , respectively, which are comparable to the estimated value for the latter in the literature . Remarkably, the intensity of the phosphorescence of ( R )‐ 1 was much stronger than that of menadione under comparable conditions, and this explains a very efficient photoreaction of this substrate, at least in part.…”

“…The phosphorescence spectra of (R)-1 and menadione (as a reference) were recorded in dichloromethane matrix at 77 K (Figure 4), affording the triplet energies of 240 and 241 kJ mol À 1 , respectively, which are comparable to the estimated value for the latter in the literature. [31] Remarkably, the intensity of the phosphorescence of (R)-1 was much stronger than that of menadione under comparable conditions, and this explains a very efficient photoreaction of this substrate, at least in part. The electron transfer mechanism was turned out to be quite unlikely for (R)-1, as the free energy change for the possible electron transfer process between triplet excited state of naphthoquinone moiety and vinyl ether in acetonitrile, estimated from the Rehm-Weller equation, [32] is somewhat endergonic, ΔG ET being + 51 kJ mol À 1 by employing the following parameters: E red (menadione) = À 0.81 V (vs SCE), [20] and E ox (ethyl vinyl ether) = 1.99 V (vs SCE).…”

Photochemical [2+2] cycloaddition reaction of enone derivatives with 2-silyloxy-1H-pyrrole derivatives

“…In general, regarding the product selectivity, cyclobutane versus oxetane, mixtures of oxetane and cyclobutane were formed in the photochemical cycloaddition reactions reported previously. [44][45][46][47][48][49][50] However, on irradiation of 1 with 5 the formation of the oxetane product 8 was observed, and the alternative possible cyclobutane products were not observed in the photo-reaction. The high pressure Hg lamp (300W) through Pyrex filter was found to be better light source than the 365 nm LED lamp for the reaction (entries 1,2, Table 2).…”