Phenanthrene aryne

THF at room temperature to produce substituted phenylallenes (231). Various arynes and terminal and internal alkynes can be used. The reaction of alkyne without propar-gylic hydrogen gave an acetylenic C-H addition product (a phenylalkyne) and a dehydro-Diels-Alder product (a phenanthrene).266... 

The same authors have also reported the reactions of other arynes with thiophen and the reactions of benzyne with 54.57,58 They present speculative reaction mechanisms to account for the formation of products, which in many cases are imperfectly identified from mass spectra alone. For example, although they acknowledge an inability to distinguish between anthracene and phenanthrene,58 they claim, in the same article, both of these as products of distinct reactions of benzyne with 54. Two minor products are claimed to be 59 and 60, respectively, and to provide evidence for the intervention of 2,3-dehydrobenzo[h] thiophen (58). 

With co-presence of Arl, alkynes, TlOAc and (dba)2Pd in the reaction pot in which the aryne is generated, multicomponent coupling directed toward phenanthrenes is realized/ ... 

The same chemoselectivity is observed in the reaction of substituted arynes with DMAD [63]. The cocycloaddition of 4,5-difluorobenzyne (62), when promoted by Pd(PPh3)4, affords phenanthrene 105 as major product (64%), accompanied by minor amounts of naphthalene 106 (8%) and hexafluorotriphenylene (63, 8%). However, using Pd2(dba)3 the selectivity is inverted, naphthalene 106 being obtained in 54% yield and phenanthrene 105 in 9% yield (Scheme 23). 

Yamamoto and co-workers developed a catalytic system [Pd(OAc)2/P(o-tol)3 in CH3CN, 60 °C] which turns out to be especially useful for cocycloaddition of electron-rich alkynes and arynes [68]. It allows phenanthrenes 116e-h to be obtained in reasonable yields, accompanied by only trace amounts of tripheny-lene (56, Table 4). 

Pd-catalyzed cocyclization of arynes with alkynes also proceeds smoothly. Yamamoto obtained phenanthrene derivatives exelusively in good yield, regardless of the electronie nature of the alkynes using Pd(OAe)2 and P(o-Tol)3. The reaction of 251 with 4-octyne gave rise to the phenanthrene 263 [82], Similarly, Perez carried out the reaction of benzyne with electron-dehcient alkynes such as dimethyl acetylenedi-carboxylate (DMAD) (264), and obtained the phenanthrene 265 as the main product using Pd(PPh3)4. On the other hand, when Pd2(dba)3 was used, the naphthalene derivative 266 was the main produet [83]. 

The polycyclic arynes derived from phenanthrenes 267,269, and 271 underwent cocyclization with two molecules of DMAD, giving the tetraesters 268, 270, and 272, respectively, in good yield [84,85]. 

Alkynes have been reported to participate in cocyclization with arynes under the same reaction conditions, affording a mixture of phenanthrenes 218, naphthalenes 219 and triphenylenes (Scheme 12.62) [115]. The chemoselectivity depends on both the palladium catalyst and the alkyne substrate used. For example, when dimethyl acetylenedicarboxylate (DMAD) is employed as the alkyne, a remarkable chemoselectivity is achieved by appropriate selection of the... 

The nature of the ligand on palladium in these complexes is thought to be the cause of the observed differences in chemoselectivity. When Pd(PPh3)4 is used, an intermediate complex 220 is observed and isolated (Figure 12.4) this complex is assumed to be involved in formation of the phenanthrenes 218. On the other hand, Pd2(dba)3 is assumed to form a palladacyclopentadiene complex 221 by oxidative coupling of two molecules of DMAD, which leads to formation of the naphthalenes 219 upon reaction with one molecule of aryne [117]. 

To increase further the variability, methods starting from three or more reaction partners have been developed, lodobenzene derivatives can be combined with an alkyne as well as an in situ formed aryne species under Pd-catalysis to efficiently form the phenanthrene core 154 (Scheme 39) [96],... 

Polycyclic Arenes. Trimethylsilylphenyl triflates have found widespread use as benzyne precursors in the preparation of polycyclic arenes. Triphenylenes are made via paUadium-catalyzed [2 + 2 + 2] cyclotrimerization of arynes, by paUadium-catalyzed annulation of the aryne and 2-halobiaryls, or via carbopalladation/carbocycUzation of arynes with substituted iodobenzenes (eq 2). All three approaches furnish substituted triphenylenes in high reported yields. Substituted phenanthrenes or naphthalenes are similarly prepared using 2-(trimethylsilyl) phenyl triflate as an aryne precursor. Treatment of the reagent with fluoride, a palladium catalyst, and a deactivated alkene, allyl halide, or internal aIk5Tie provides 9-substituted or 9,... 

Guitian et al. also reported the first cocycUzation of arynes with alkynes such as dimethyl acetyl-enedicarboxylate (DMAD) leading to phenanthrenes 101 or naphthalenes 102. The selectivity of the process can be tuned by an appropriate choice of the catalyst (Schane 12.52) [90]. These authors have also described the first enantioselective version of this process, using a Pd-(BINAP) complex as catalyst, although the nonracemic 9,12-dimethoxypentahelicene 103 was isolated in a modest yield but with reasonable ee (Scheme 12.52) [91]. Diynes can also participate in [2+2+2] cycloaddition with arynes as demonstrated by Mori et al. in the total synthesis of taiwanins C and E 104a and b (Scheme 12.52) [92]. 

Carbopalladation of Arynes by n-Allylpalladium and Related Complexes. Pioneering work from Yamamoto established that ji-allylpalladium species are particularly effective for the carbopalladation of arynes leading to an arylpalladium intermediate 109, which can be employed in three-component couplings with a second aryne to give phenanthrenes such as 110, or with alkynes to produce naphthalenes such as 111. In the first case, 109 evolves through insertion of another benzyne (1) molecule (carbopalladation of 1 by an arylpalladium) and further carbopalladation of the pendant alkene to afford a tricyclic species that undergoes p-hydride elimination (Scheme 12.55) [96],... 

In this field, Cheng et al. have also developed the carbocyclization reaction of aromatic iodides, bicyclic alkenes, and arynes to afford various armulated 9,10-dihydrophenanthrene derivatives 117 (Scheme 12.58) [102]. A related eross-coupling of arynes with aryl iodides but using alkynes as the third component has been described by Larock and Liu, furnishing substituted phenanthrenes 118 (Scheme 12.58) [103]. 

SCHEME 3.18 Palladium-catalyzed carbocyclization of aryl iodides, bicyclic alkenes, and arynes. Synthesis of annulated 9,10-dihydro-phenanthrenes. 

SCHEME 3.19 Synthesis of phenanthrenes via palladium-catalyzed cross-coupling of aryl halides, acetylenes, and arynes. 

T. Zhang, X. Huang, L. Wu, A facile synthesis of 2H-chromenes and 9-functionalized phenanthrenes through reactions between a,p-unsaturated compounds and arynes, Eur. J. Org. Chem. (2012) 3507-3519. 

The same group reported the efficient synthesis of polycyclic aromatic compounds by the palladium-catalyzed [2 - - 2 - - 2] cycloaddition of arynes with alkynes (Scheme 6.10) [12d,13]. The reactions of aryne precursor 29 and alkyne 30 afforded phenanthrenes 31 (aryne/alkyne = 2 1) as a major product. The use of electron-rich... 

Even electron-rich alkynes 34 reacted with aryne precursor 33 to give the corresponding phenanthrenes 35 in good yields. 

Allyl chlorides can be employed in place of alkynes for the palladium-catalyzed [2-I-2-I-2] cycloaddition of arynes, as reported by Yamamoto et al. in 2000 [16]. Substituted allyl chlorides 40 reacted with aryne from 39 accompanying the elimination of HCl in the presence of a paUadium(0) catalyst and CsF to produce phenanthrenes 41 and 42 in good yields, although the regioselectivity was moderate (Scheme 6.13). A mechanism that has been proposed involves a cascade-type addition of -ir-allylpalladium complex onto two benzynes. In the presence of additional alkynes 44, three-component cycloaddition product 45 was obtained in good yields with complete regioselectivity (Scheme 6.14). 

The reactions of arynes with allenes followed by olefln isomerization produces 9,10-disubstituted phenanthrenes. In 2007, Li et al. reported that electron-deficient allenes 47 react with arynes from 46 in the presence of [(allyl)PdCl]2/P(o-tol)3 catalyst and CsF to produce phenanthrenes 48 (Scheme 6.15) [17]. 

In 2000, Yoshikawa et al. reported synthesis of phenanthrenes 26 by palladium-catalyzed three-component annulation (allyl chloride 25-aryne-aryne) (Scheme 28.10) [14]. Intramolecular carbopalladation to an alkene moiety in arylpal-ladium(II) intermediate 28, arising from dual insertion of arynes into ir-allylpalladium... 

Cocyclotrimerization of arynes with allenes in the presence of NiBr2(dppe)-Zn afford phenanthrene derivatives in moderate to good yields [142],... 

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