- Gold-Catalyzed Cycloisomerization of Sulfur Ylides to Dihydrobenzothiepines
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The metal-promoted nucleophilic addition of sulfur ylides to π-systems is a well-established reactivity. However, the driving force of such transformations, elimination of a sulfide moiety, entails stoichiometric byproducts making them unfavorable in terms of atom economy. In this work, a new take on sulfur ylide chemistry is reported, an atom-economical gold(I)-catalyzed synthesis of dihydrobenzo[b]thiepines. The reaction proceeds under mild conditions at room temperature.
- Knittl-Frank, Christian,Saridakis, Iakovos,Stephens, Thomas,Gomes, Rafael,Neuhaus, James,Misale, Antonio,Oost, Rik,Oppedisano, Alberto,Maulide, Nuno
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- Reaction of cyclopropylcarbene-metal complexes with nucleophiles, halogens and HX
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The reaction of halogens, pseudohalogens, and HX with cyclopropyl(phenylthio)carbene-chromium complexes leads to the formation of 1,4-dihalo-1-thiophenyl-1-butene systems with a moderate-high degree of stereocontrol in the formation of the alkene. A mecha
- Reid, Margaret D.,Tirado, Liz,Zhang, Jianwei,Dike, Nwamara,Herndon, James W.
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- Improved synthesis of C8-C20 segment of pectenotoxin-2
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The C8-C20 segment of pectenotoxin-2 was efficiently synthesized in 16% overall yield in 22 steps from l-malic acid via an improved route.
- Fujiwara, Kenshu,Suzuki, Yuki,Koseki, Nao,Murata, Shun-Ichi,Murai, Akio,Kawai, Hidetoshi,Suzuki, Takanori
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scheme or table
p. 5589 - 5592
(2011/11/07)
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- Tin Radical Addition to Alkynyl Sulfides: Reactivity of the Intermediate Thioalkyl-Substituted β-(Tributylstannyl)vinyl Radicals
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Phenyl and benzyl alkynyl sulfides 1a-g and 3a, phenylalkynylamines 19a,b, ethers 22a,b, and selenide 31 reacted with tributyltin radicals to give intermediate β-stannylvinyl radicals, whose fate depended on the nature of the side chain. 4-Phenylthio-substituted but-1-en-2-yl radicals underwent stereospecific 5-exo cyclization on the adjacent phenyl ring.The resulting spirocyclohexadienyl radicals gave thiophenes and thiopyrans by carbon-sulfur bond scission or ring expansion on the exocyclic double bond, respectively.Similar behavior was exhibited by the corresponding selenium-containing radical, which afforded a selenophene almost exclusively. (Benzylthio)alkyl-substituted radicals gave products deriving from intramolecular SH2 substitution at the sulfur atom, whereas propargyl sulfides yielded a stannylallene via a β-scission reaction.No 6(or more)-membered ring closure was observed with pentynyl and hexynyl phenyl sulfides 1b,c, which gave only the (E)-addition products of tin hydride; oxygen- and nitrogen-containing vinyl radicals also gave the (E)-adducts exclusively.An interaction between the unpaired electron orbital and the empty low-energy orbitals of the heteroatom might explain why sulfur and selenium can undergo 5-exo cyclization.
- Capella, Laura,Montevecchi, Pier Carlo,Nanni, Daniele
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p. 3368 - 3374
(2007/10/02)
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- Elimination and Addition Reactions. Part 41. Nucleophilic Eliminative Fission of Cyclopropanes: the Coiled Spring Effect of Ring Strain on Nucleofugality and its Evaluation
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Rates have been measured of sulphonyl-activated eliminative ring fissions of a series of six cyclopropanes in which the leaving group is stabilised by alkoxycarbonyl, cyano, or sulphonyl groups.The measurements allow assignment of ranks (nucleofugalities) to carbon leaving groups in systems in which the connection to the leaving group is strained by incorporation in a cyclopropane ring.The values obtained are compered with those obtained for a unstrained (acyclic) analogues.Rank enhancements of about 9(log) units are obtained; these enhancements suggests that free energies of activation for leaving-group expulsion are reduced by about 53 kJmol-1, or about 46 percent of these excess of enthalpy of the strained ring, notwithstanding the small degree of ring fission in the transition structure.The effect of phenyl substitution at the leaving group suggests that cleavage of the ring is very little advanced in the transition structure, although this is variable with the nature of the leaving-group stabilisation.This is the first direct determination of the effect of strain on nucleofugality.
- Hughes, Simon,Griffiths, Gwerydd,Stirling, Charles J. M.
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p. 1253 - 1264
(2007/10/02)
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- An easy access to homopropargylic ethers
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Chloromethyl ethers, obtained from alcohols, formaldehyde and HCl, react regioselectively, as shown previously in one case by L.Miginiac, with allenyl aluminium reagents derived from propargyl bromides and aluminium, to give homopropargyl ethers.No evidence for the presence of allenyl ethers was obtained in the cases described.This condensation is used to obtain a protected acetylenic synthon 1, required for the synthesis of an ecdysteroid analogue (1).
- Guedin-Vuong, Denis,Nakatani, Yoichi
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p. 245 - 252
(2007/10/02)
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