Acenaphthylene cycloaddition

The photoaddition of acenaphthylene to cyclopentadiene was shown to be sensitive to the presence of heavy atoms in the solvent, as shown in Table 10.9. The data in Table 10.9 show that product (46) increases from 18% of the total product in cyclohexane to 38% of the total product in 1,2-dibromo-ethane. This suggests that the [4 + 2] cycloaddition products (47) and (48) and the [2 + 2] product (46) are produced from different excited states. Accordingly, some of the [4 + 2] product has been postulated to arise from either (a) a singlet excited state or (b) a vibrationally excited ground state... 

The photocycloaddition of maleic anhydride to acenaphthylene has been studied by Hartmann and Heine.(107a> Irradiation of acenaphthylene in the presence of maleic anhydride in light-atom solvents (dioxane, acetone, or acetonitrile) yields only dimers or copolymers of acenaphthylene. In heavy-atom solvents (dichloromethane, dibromomethane, or iodomethane), however, dimerization is suppressed and cycloaddition with maleic anhydride predominates ... 

Similarly, the irradiation of acenaphthylene in the presence of bromomaleic anhydride in ethyl bromide leads to cycloaddition.<1070> No adduct was... 

The meso-ionic l,3-dithiol-4-ones (134) participate - in 1,3-dipolar cycloaddition reactions giving adducts of the general type 136. They show a remarkable degree of reactivity toward simple alkenes including tetramethylethylene, cyclopentene, norbomene, and norbor-nadiene as well as toward the more reactive 1,3-dipolarophilic olefins dimethyl maleate, dimethyl fumarate, methyl cinnamate, diben-zoylethylene, A -phenylmaleimide, and acenaphthylene. Alkynes such as dimethyl acetylenedicarboxylate also add to meso-ionic 1,3-dithiol-4-ones (134), but the intermediate cycloadducts are not isolable they eliminate carbonyl sulfide and yield thiophenes (137) directly. - ... 

Hamaguchi and Nagai (65,66) generated oxamiinchnones 109 as described in Section 10.1.7. They find that in addition to a cycloaddition with DMAD (Scheme 10.20), these oxamiinchnones react with acenaphthylene, maleimides, phenylacetylene, and dibenzoylacetylene to afford 335-338, respectively, in good yields (65,66). In the case of 335 and 336 the exo/endo ratio varies from 3 2 to 5 1 depending on the substituents. 

Photochemical cycloaddition of cyclohex-2-ene-l,4-dione (31) and acenaphthylene (32) in dichloromethane gives the iM-,un//,c -adduct 33 in 15% yield, in addition to large amounts of acenaphthylene dimers, which are insoluble and precipitate during the photolysis.100... 

Acenaphthylene, indene, and styrene undergo periselective 4 + 2-cycloaddition with 3-ethoxycarbonyl-2//-cyclohepta[Z>]furan-2-one in high yield.152... 

Acenaphthylene dibromide (147) was also reduced to produce acenaphthylene (148) in quantitative yield (equation 85). A similar result was reported by Inesi and collaborators129, and confirmed again by others130. Four-electron reduction of ortho-xylylene tetra-bromide (149) gives the same stable product, 146, deduced to arise from benzocyclo-butadiene following a [4+2] cycloaddition and retro[2+2] rearrangement to rearomatize. 

Surprisingly, some Diels-Alder cycloaddition reactions show no variation in endojexo product ratio with changes in solvent phase. Ordered liquid-crystalline solvents are not able to differentiate between endo- and exo-activated complexes in the Diels-Alder reaction of 2,5-dimethyl-3,4-diphenylcyclopentadienone with dienophiles of varying size (cyclopentene, cycloheptene, indene, and acenaphthylene), when it is carried out in isotropic (benzene), cholesteric (cholesteryl propionate), and smectic liquid-crystalline solvents at 105 °C [734]. 

Acenaphthylene forms [2 + 2]-cycloaddition products with electron-deficient alkenes such as acrylonitrile and methyl acrylate (Nakamura et al., 1978). Cycloaddition is favoured by carrying out the reaction in a micellar solution owing to the inefficiency of the dimerisation in such an organised system. 

Scheme 9.1. [2 -r 2] cycloaddition with formation of acenaphthylene 101 and phenanthrene 102... 

The latter compound is similar to 60 (R = C02Et) in reactivity toward acenaphthylene, undergoing [4 + 2]-cycloaddition/cheleotropic elimination to the known sulhnylamine Et02C—N=S=0, which was sufficiently stable to be isolated but underwent facile cycloaddition with 2,3-dimethyl-1,3-butadiene to give the thiazine sulfoxide 65. Although 64 is a fairly reactive molecule, the reactivity in cycloaddition reactions is less than that of 60, which is in keeping with the known differences in reactivity of thiophene 1-oxide and thiophene 1,1-dioxide. 

When l,8-bis(dimethylamino)-4-vinylnaphthalene (121) is heated with 3,6-diphenyl-s-tetrazine (DFT), a [4 + 2]-cycloaddition reaction with reverse electron demands takes place to give the 1,4-dihydropyridazine derivative 208 (Scheme 37). The latter could be oxidized with chloranil or with excess of DFT to pyridazine 209118. A similar reaction with acenaphthylene proton sponge 107 gives directly the annelated pyridazine 139, since the intermediate dihydropyridazine is readily oxidized in air. It was established that the reactivity ratio of compounds 107, 121, 5-dimethylaminoacenaphthylene and acenaphthylene in the reaction with DFT is equal to 32 17 14 1, respectively. These data are in... 

Rate data have been obtained from a detailed analysis of the previously reported 1420 maximum and fall off in the photodimerization of acenaphthylene with increasing concentrations of dissolved ethyl iodide.1420 The heavy-atom solvent dibromomethane facilitates the cross cycloaddition of acenaphthylene to trans- and cw-penta-1,3-diene by inducing intersystem crossing to the triplet state of the aromatic hydrocarbon. The intermediacy of a biradical is proposed and the stereospecificity can be understood in terms of the maintenance of the stereochemical integrity of the allylic radical units.143... 

Cycloadditions of tetrazines 1 to acenaphthylenes 209 have also been reported (Scheme 53) <2003RCB218>. 

It has subsequently been shown <86TL1105> that (146) and (147) are unique only in regard to their stability and not with respect to attack of nitrene at the sulfur atom. In a reinvestigation of the reaction of ethyl azidoformate with several thiophenes it has been shown that S,N-ylides are indeed formed as transient products in every case these could be trapped by cycloaddition with acenaphthylene (see Section 2.10.3.3) leading to fluoranthene derivatives. 

Oxidation of the S,N-ylide (146) with MCPBA gave the product (225) in 84% yield. This sulfoxilimine corresponds to the thiophene-1,1-dioxide. This compound also undergoes the expected [4 -I- 2]cycloaddition with acenaphthylene followed by cheletropic extrusion, leading to the same product as with the parent S,N-ylide <86JCS(P1)233>. 

In contrast, the S,C-ylide (139a) prepared from tetrachlorothiophene and diazomalonic ester under rhodium acetate catalysis undergoes cycloaddition with acenaphthylene much more slowly however, after heating at 80 °C for 7 h, the reaction leads to the aromatized fluoranthene (226) in 97% yield. The formation of (226) involves a proton shift and loss of chlorine the exact mechanism and the location of the chlorine atoms are not clear <86JCS(Pl)233>. 

When xanthenethione (38) is excited to its ,7r -state, [2 + 2]cycloaddition proceeds with bis(alkylthio)ethyne. The cyclo-adduct [(42) or (43)] is in thermal equilibrium with its open isomer [(44) or (45)]. A similar reaction of (37) with acenaphthylene, indene, or A-phenylmaleimide affords a spirothietan derivative in good yield. Thioxanthenethione in the ,7r -state cyclo-adds to alkyl- or alkoxy-substituted butatrienes, giving the thietans (46)—(49). ... 

Photocycloadditions are also exploited in the synthesis of fused polycyclic compounds. Tetracyclic (4-hetera)cyclopent[, c]acenaphthylenes can be synthesized by light-induced cycloaddition of 4-alk-l-ynylcoumarins to 2,3-dimethylbut-2-enes (Scheme 6.33). Addition of triplet-excited 4-alk-l-ynylcoumarin to the alkene affords the triplet biradical, which undergoes 1,5-cyclization to cyclopentenylcar-bene. The latter undergoes electrocyclic ring closure and [1,9]-H shift to yield the product [37]. 

---