- Sigmatropic Rearrangements of Hypervalent-Iodine-Tethered Intermediates for the Synthesis of Biaryls
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Metal-free dehydrogenative couplings of aryliodanes with phenols to afford 2-hydroxy-2′-iodobiaryls have been developed. This reaction proceeds through ligand exchange on the hypervalent iodine atom followed by a [3,3] sigmatropic rearrangement and with complete regioselectivity. This coupling, in combination with in situ oxidation by mCPBA, enables the convenient conversion of iodoarenes into desirable biaryls. The obtained biaryls have convertible iodo and hydroxy groups in close proximity, and are thus synthetically useful, as exemplified by the controlled syntheses of π-extended furans and a substituted [5]helicene. DFT calculations clearly revealed that the rearrangement is sigmatropic, with C?C bond formation and I?O bond cleavage proceeding in a concerted manner. Acetic acid, which was found to be the best solvent for this protocol, renders the iodine atom more cationic and thus accelerates the sigmatropic rearrangement.
- Hori, Mitsuki,Guo, Jing-Dong,Yanagi, Tomoyuki,Nogi, Keisuke,Sasamori, Takahiro,Yorimitsu, Hideki
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- Photostimulated Reactions of o-Dihalobenzenes with Nucleophiles Derived from the 2-Naphthyl System. Competition between Electron Transfer, Fragmentation, and Ring Closure Reactions
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The photostimulated reaction of o-dihalobenzenes 2 with 2-naphthoxide ions 1-O gave the substitution product on carbon 1 of the naphthyl moiety with retention of halogen (I, Br, and Cl) 3 as well as the ring closure product benzonaphtholfuran (4), with product 3 being an intermediate in the formation of 4.The products obtained in the photostimulated reaction of 2-naphthalenethiolate ions 1-S with 2 depend on the halogens.When both nucleofugal groups are iodine, only the ring closure product benzonaphthothiophene (10) is obtained.With o-bromoiodobenzene, the photostimulated reaction gave 10 and the substitution product on sulfur with retention of bromine, while with o-chloroiodobenzene the only observed product was the substitution product on sulfur with retention of chlorine.The photostimulated reaction of 2 with 2-naphthaleneselenolate ions 1-Se gave the same amount of cyclized product benzonaphthoselenophene (14) and the substitution product on selenium without retention of halogen 15, although in an overall low yield.It is suggested that all these reactions occur by the SRN1 mechanism.Theoretical studies support the different behavior found with the nucleophiles derived from the 2-naphthyl system.
- Baumgartner, Maria T.,Pierini, Adriana B.,Rossi, Roberto A.
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- The reactivity of oxygen nucleophiles with aryl radicals in the S(RN)1 mechanism
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The photostimulated reaction of 2-naphthoxide ions 1 with o-dihalobenzenes in liquid ammonia gives the halosubstituted product 4 and the cyclized substituted product 5. This is the first report about the coupling of an aromatic σ radical with an oxygen functionality in the chain propagation cycle of the S(RN)1 mechanism.
- Baumgartner,Pierini,Rossi
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- Pd(0)-catalyzed chemoselective construction of spirocarbocycles via an alkyne insertion/β-naphthol dearomatization cascade
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A microwave-assisted Pd(0)-catalyzed alkyne migratory insertion/β-naphthol dearomatization cascade process has been accomplished to access a variety of spirocyclic compounds bearing all-carbon quaternary stereogenic centers in high yields with excellent chemoselectivities.
- Zheng, Huayu,Bai, Lu,Liu, Jingjing,Nan, Jiang,Zuo, Zhijun,Yang, Liu,Wang, Yaoyu,Luan, Xinjun
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p. 3061 - 3064
(2015/06/08)
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