- Highly chemoselective synthesis of aryl allylic sulfoxides through calcium hypobromite oxidation of aryl allylic sulfides
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A highly chemoselective oxidation of widely substituted aryl allylic sulfides, prepared by allylation of arylthioethers with KF-Celite, to the corresponding aryl allylic sulfoxide was achieved by employing calcium hypobromite. Neither over-oxidation to sulfones nor halogenation of the aromatic rings was observed. The protocol may be successfully applied for the oxidation of substituted allylic systems (i.e., 2-haloallyl) that per se could interact with the oxidizing agent.
- Pace, Vittorio,Castoldi, Laura,Holzer, Wolfgang
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supporting information; experimental part
p. 967 - 972
(2012/03/11)
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- Neighbouring-group influence on the ring opening of 2-aryloxymethyl-1,1,2-tribromocyclopropanes under phase-transfer conditions
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When a number of 2-aryloxymethyl-1,1,2-tribromocyclopropanes were treated with sodium hydroxide and ethanol under phase-transfer conditions, ring opening occurred to give mixtures of acetylenic diethyl acetals and ketals in better than 80% total isolated yield. The acetylenic diethyl ketals predominated significantly and were, in some cases, almost the exclusive product. It is argued that this ketal selectivity is in part caused by hydrogen bonding between ethanol and the aryloxy group.
- Bakstad, Einar,Olsen, Are S.,Sandberg, Marcel,Sydnes, Leiv K.
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p. 465 - 472
(2007/10/03)
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- Cyclizations and Rearrangements of Samarium Diiodide-Generated Vinyl Radicals
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Vinyl bromides 1, 5, 15, 20, 23, 27, 33a,b, 41a-c, 44a-c, 46a,b, 52a,b, 55a, 56a,b, and 60a,b react with samarium diiodide in THF and/or acetonitrile to give the corresponding vinyl radicals.Radicals 3, 7, and 16 afforded products deriving from cyclization on the adjacent triple bond in a 5-(?-exo)exo, 6-(?-endo)exo, and 6-(?-exo)exo mode, respectively.Radical 7 undergoes competitive 1,5-hydrogen translocation.Vinyl radicals 21 and 24 readily cyclize on the proximal double bond, leading to 5- and 6-membered rings, respectively.Thienyl-substituted radical 28 leads to a product deriving from 5-exo cyclization on the thiophene ring and subsequent β-fission of the C-S bond, whereas thienyl-substituted radicals 34a,b undergo almost exclusively 1,5-hydrogen translocation.Aryl-substituted radicals obtained from vinyl bromides 41, 44, 46, 52, and 55 do not form any products deriving from 5-exo or 6-exo cyclization (or ipso cyclization).Finally, naphthyl-substituted radicals 57a and 61a give only direct reduction products, whereas the radical 61b affords, in addition to the direct reduction product, a rearranged product deriving from a 1,3-radical migration of the naphthylthio group.Evidence is reported for the reduction of EWG-substituted benzene rings and thio-substituted naphthalene rings to radical anions, which can fragment on the side chain with the elimination of allyl radicals. α-Oxy(and α-thio)-substituted radicals deriving from 1,5-shift rearrange to alcohols (and thiols) through a Wittig rearrangement or a cyclization/fragmentation process.
- Capella, Laura,Montevecchi, Pier Carlo,Navacchia, Maria Luisa
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p. 7424 - 7432
(2007/10/03)
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- New reagents for radical allylations
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Three reagents are introduced for radical allylations: 3-phenylthio-2-bromopropene, 2,3-bis(trimethylstannyl)propene, and 3-tris(trimethylsilyl)silylthiopropene.
- Curran,Yoo
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p. 6931 - 6934
(2007/10/02)
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