Dibenzo cycloaddition

As a consequence of the rigid face-to-face orientation, there are strong electronic interactions between the benzene rings in the dibenzo-anellated isodrin derivative. Irradiation with 254-nm UV light gave rise to a 7 3 equilibrium mixture of the educt with the [6 -I- 6]cycloaddition isomer. At an irradiation wavelength of 300 nm the cycloaddition wa completely reversed. 

Cationic complexes of rran.s-chelating tridentate ligand, (/ ,/ )-4,6-dibenzo-furandiyl-2,2 -bis(4-phenyloxazoline), with transition metal(II) perchlorates as effective catalysts for asymmetric cycloaddition of nitrones 98YGK368. 

In contrast, cycloaddition of the thiazuleno derivative 9, prepared from dibenzo[fr,/]thiepin-10,11-dione (2), with diphenylacetylene yields 77% of the same product 8.94 Other cycloadducts from 9, and from its S, 5-dioxide, were also obtained in good yields. 

By analogy with the formation of3//-azepines by cycloaddition of 2//-azirines withcyclopenta-dienones, l,3-diphenyl-2//-inden-2-one (58) and its dibenzo analog 60 enter into [4 + 2] cycloadditions with 27/-azirines to give 3//-2-benzazepines 59 and phenanthro[9,10-e]azepincs 61, respectively.96... 

F-Dibenz[/),/]azepines enter into 1,3-dipolar cycloadditions with diarylnitrilimines 14, generated in situ from hydrazonyl chlorides, to give dibenzo[7>,/]pyrazolo[3,4-rf]azepines, e.g. 15, in good yields.233... 

As vinylbenzofurans allow a large variety of substituted dibenzofurans to be synthesized, 2- and 3-vinylbenzo[b]thiophenes allow an easy entry, by Diels Alder reaction with the appropriate dienophiles, to substituted dibenzo-thiophenes which are not easily accessible by other methods. Vinylbenzo-[bjthiophenes are less reactive than the corresponding vinylbenzo[b]furans. Some cycloaddition reactions of 2-vinylbenzo[b]thiophene (82) with various dienophiles are reported [83] in Scheme 2.34. 

A dibenzo[fc,react with benzyne, confirming that the [4+2] cycloaddition is preferred to the [2+2] mode <96TL8883>. 

Table 16 Polar cycloadditions of dibenzo[c,e]-[1,2]-thiazinylium salt 97 with 1,3-butadienes 41 (Equation 27)...

Dipolar cycloaddition is another route to benzopyrrolo[l,2-a]azepines by pyrrole ring formation. The azomethine ylide derived from imine 88 and difluorocarbene adds to DMAD to produce dimethyl 3-fluoro-9H-dibenzo[c,/]-pyrrolo[l,2-fl]azepine-l,2-dicarboxylate 89 in 20% yield (Equation (12)... 

The polar cycloaddition of the in rr / -prepared 1,2-thiazinylium salt 20 from Woxide 80 vide infra) with 2,3-disubstituted butadienes 81a and 81b affords adducts 82a and 82b (Scheme 11) <1999TL95>. Mono- and disubstituted salts 42 and 83 are more stable than the diphenyl-1,2-thiazinylium salt 20 and can in fact be isolated. These dienophiles undergo [4-1-2] cycloaddition reactions with butadiene 81a affording products 84a and 84b with a different regioselectivity than dibenzo-1,2-thiazinylium salts 82a and 82b <1999TL1505, 2001TL4183>. 

Photocycloadditions of naphthalene derivatives to alkcnes have been recently reviewed.60 Examples of such reactions are the photocycloaddition of naphthalene to 2,3-dihy-drofuran,61 of 4-methoxy-l-naphthonitrile to acrylonitrile62 and of 2-trimethylsiloxynaph-thalene to methyl acrylate.63 2-Naphthols undergo cycloaddition with ethene in the presence of aluminum trihalides only.64 Other bicyclic aromatic compounds, e.g. A-acylindoles65-67 and /V-methylphenanthrene-9,10-dicarboximide,68 have also been studied in detail. Irradiation of 5/f-dibenzo[u,i7]cyclohepten-5-one (21) and dimethyl 2-methylfumarate (22) in dioxane gives the cyclobutane adduct 23 in 73% yield.69... 

Several dibenzo[6,tf ]pyran-6-ones (360) have been prepared by the reaction of substituted phenols with 2-methoxycarbonyl-l,4-benzoquinone in the presence of trifluoroacetic acid (79HCA2833). Treatment with silver oxide converts the products into the related quinones which may be elaborated to benzo[6]naphtho[[Pg.800]

DFT calculations on the intramolecular Diels-Alder reaction of penta-l,3-dienyl acrylates predict stereoselectivities that are in good agreement with the experimen- (g) tal results.85 Another DFT study at the B3LYP/6-31G(d) level of the intramolecular Diels-Alder cycloaddition of 5-vinylcyclohexa-1,3-dienes has been reported. Reaction rates are influenced by dienophile twisting and substituent effects.86 The intramolecular dehydro-Diels-Alder reactions of ynamides (79) provides a new synthesis of benzo[fc]-, tetrahydrobenzo[fc]-, naphtho[l,2-/j -, and dibenzo[a,c]carbazoles... 

Benzyne generated at room temperature from phenyl[2-(trimethylsilyl)phenyl]iodonium trifluoromethanesulfo-nate has been trapped in a [4+2] cycloaddition reaction with diarylthiones. The initial product, a 6-aryl-477 dibenzo[, r/]thiopyran, is accompanied by 6-aryl-67/-dibenzo[, r/]thiopyran arising by 1,3-prototropic aromatization of the cycloadduct (Equation 114). The use of sterically congested thiones, such as thiopivalophenones, results in competition from a [2+2] cycloaddition and 2/7-benzo[A]thietes are the sole products <2000BCJ155>. 

The dibenzo derivatives (103 R2 = H) similarly undergo electrophilic substitution and cycloaddition reactions. Typically, under Vilsmeier-Haack conditions the 7-formyl (103 R2 = CHO) and the 7-acetyl (103 R2 = COMe) derivatives are formed from the unsubstituted compounds (103 R2 = H). With strong acids the dibenzo compounds (103) form salts (73CL175). 

Furthermore, Z-3-bromo-propcnoates 148 are suitable substrates for Sonogashira-[4 + 2]-cycloadditions to furnish 6H-dibenzo[M]pyran-6-ones 149 in moderate to excellent yields as shown by Yamamoto and... 

Azoniafulvene, cycloaddition to hydrazones, 59, 49 2a-Azoniahexahelicene, 55, 307 5a-Azonianaphthacene, see Dibenzo[b,g]quinolizinium l2b-Azoniaperylene, see Isoindolo[ 1,2,3-r/elquinolizinium... 

Benzo[c]furans undergo [4 + 4] cycloaddition to give 5,6,ll,12-tetrahydro-6,ll-epoxy-dibenzo[A/][l,4]diazocincs, which are thermally decomposed to 2//-benzimidazoles7. 

Very stable polycylic phosphiranes were obtained by an intramolecular cycloaddition reaction of aminodichloro-phosphines with the C-C double bond of 577-dibenzo[ , [7]annulene (dibenzocycloheptene) under the influence of Mg-turnings. Formally, these compounds are formed by an intramolecular [2-Fl] cycloaddition of an R2N-P phosphinidene unit to the C-C double bond of the central seven-membered ring. In analogy to the hydrocarbon barbalan the amino compound is named BARBAR-Phos <1999AGE1623>. In a comparable reaction sequence, dibenzophosphasemibullvalene was obtained (Equation 25) <2003AGE3955>. 

The results of the reactions involving these carbenes are compiled in Table 14. Irradiation of 5-diazo-10,l l-dihydrodibenzo[a,c/]cycloheptene with a high-pressure mercury lamp gives 10,11-dihydrodibenzo[a,rf]cyclohepten-5-ylidene, which can be trapped under the right conditions. When the photolysis was carried out in the presence of ( )-l-phenylprop-l-ene, stereospecific cycloaddition took place to give rra i-3-methyl-l-phenylspiro[cyclopropane-2,5 -10, lT-dihydro-5 //-dibenzo[a,cf]cycloheptene in 19% yield.Efficient trapping even on a synthetic scale is experienced when the diazo compound is irradiated in various styrenes. Thus, when 4-methoxystyrene was used as solvent l-(4-methoxyphenyl)spiro[cyclopropane-2,5 -10, lT-dihydro-5 7/-dibenzo[a,ii]cycloheptene (1) was isolated in 81% yield in addition 5,5 -bi(10,ll-dihydro-5//-dibenzo[u, f]cycloheptyl) (2) was obtained in 11% yield. 

Tominaga and coworkers 22 prepared dimethyl dibenzo[a,/t]cycl[3.2.2]azine-l,2-dicar-boxylate (553) by an [8 -I- 2] cycloaddition reaction of l-cyanoisoindolo[2,l-o]isoquinoline (552) with dimethyl acetylenedicarboxylate (57), followed by elimination of HCN. A small amount of acetic acid was added to improve the yield of the reaction from 1% to 26%. The double adduct 554 was isolated in minor amounts (equation 159). 

The photochemical cycloaddition of 4-methyl-l,2,4-triazoline-3,5-dione to the dibenzo-cyclooctatetraene 289 yields 3.5% of the cycloadduct 290, together with 36% of 291, the product of a di-jr-methane rearrangement (equation 153. Anthrasteroids 293 (R = H, Ac or COPh) are produced in an oxidative rearrangement when the phenyltriazoline-dione adduct of 292 is treated with boron trifluoride etherate. The 5,7-diene system of ergosteryl acetate 294 can be protected by cycloadduct formation, allowing selective hydrogenation of the 22,23-double bond " ... 

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