Réactions des cycloproparènes avec des métaux de transition

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The rhodium(II)-catalyzed aziridination of olefins with {[(4-nitrophenyl)sulfonyl]imino}phenyl-lambda³-iodane

The aziridination of olefins with {(4-nitrophenylsulfonyl)imino}phenyl-l3-iodane, NsNTIPh (1c), in the presence of [Rh2(OAc)4] proceeds in yields of up to 85% when the olefin is used in large excess. Under optimized conditions, styrene (4a) is aziridinated with 1 equiv. of NsNTIPh (1c) in 64% yield with 2 mol% of catalyst. The aziridines derived from electron-rich olefins undergo ring-opening under the conditions of the aziridination and afford rearrangement products or pyrrolidines. The aziridination is sterospecific with 1,2-dialkyl- and 1,2-arylalkyl-disubstituted olefins, but nonstereospecific with stilbene.The r-value for aziridination of substituted styrenes is 0.61. No ring-opened products are observed upon aziridination of vinylcyclopropanes. In the presence of chiral RhII catalysts, the aziridination is enantioselective, affording an ee of 73% with cis-b-methylstyrene (4k) and Pirrungs [Rh2{(R)-()-bnp}4] catalyst. The experimental results are consistent with a one-step mechanism for transfer of the nitrenoid moiety from the catalyst to the olefin

[1,1-bis (trimethylsilyl)]-1<i>H</i> -cyclopropa [<i>b</i>] napththalene[tricarbonyl-chromium]: the first arene-chromium complex of a cycloproparene

[1,1-Bis (trimethylsilyl)]-1H-cyclopropa [b] naphthalene rricarbonylchromium (2) was synthesized by reaction of 1,1-bis (trimethylsilyl) cyclopropa [b] naphthalene (1b) with tricarbonyltris(acetonitrile) chromium.</p

The Decomposition of <i>cis</i>-Fused Cyclopenteno-1,2,4-trioxanes Induced by Ferrous Salts and Some Oxophilic Reagents

Two cis‐fused cyclopenteno‐1,2,4‐trioxanes, 1a and 1b, were subjected to Zn in AcOH or FeCl₂·4H₂O in MeCN. In the first case, the main course was deoxygenation to give cyclopentanone (18) and the 1,4‐diphenyl‐ or 1,4‐bis(4‐fluorophenyl)cyclopent‐3‐ene‐1,2‐diol 10 (Scheme 5). In the second case, isomerization chiefly occurred resulting in the formation of a dimer 9 of the respective 3,5‐diaryl‐5‐hydroxycyclopent‐2‐enyl 5‐hydroxypentanoates 8 (Scheme 3)

Rhodium(II)-Catalyzed CH Insertions with {[(4-Nitrophenyl)sulfonyl]imino}phenyl-λ³-iodane

The [Rh₂(OAc)₄]‐catalyzed decomposition of {[(4‐nitrophenyl)sulfonyl]imino}phenyl‐λ³‐iodane (NsN=IPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by O‐substituents. Scope and limitations of the reaction were investigated. Yields of up to 84% were achieved in the most favorable cases. Yields were enhanced by electron‐releasing substituents and decreased by steric hindrance. Aziridination competed with allylic insertion with olefinic substrates. The insertion reaction proceeded with retention of configuration. With chiral RhII catalysts, a modest asymmetric induction was observed. A mechanism involving direct insertion by a Rh‐complexed nitrene into the CH bond is proposed

The Deoxygenation and Isomerization of Artemisinin and Artemether and Their Relevance to Antimalarial Action

The treatment of artemisinin (1) and ß-artemether (6) with Zn dissolving in AcOH for a few hours results in mono-deoxygenation giving deoxyartemisinin (5) and deoxy-ß-artemether (7), respectively, as the sole product. In contrast, submission of 1 to FeCl2 · 4 H2O in MeCN at room temperature for 15 min causes only isomerization, (3aS,4R,6aS,7R,10S,10aR)-octahydro-4,7-dimethyl-8-oxo-2H-10H-furo[3,2-i] benzopyran-10-yl acetate (8) and (3R)-3-hydroxydeoxyartemisinin (9) being produced in 78 and 17% yield, respectively. The action of FeCl2 · 4 H2O in MeCN on 6 is similar. Under the same conditions, 6 gives products analogous to 8 and 9 accompanied by an epimeric mixture of 2-[4-methyl-2-oxo-3-(3-oxobutyl)cyclohexyl]propanaldehyde in yields of 32, 23, and 16%, respectively. No epoxide is formed on repeating the last two experiments in the presence of cyclohexene. The deoxygenation of 1 and 6 by Zn is rationalized in terms of its oxophilic nature. The catalyzed isomerization of 1 and 6 by Fe2+ is attributed to the redox properties of the Fe2+/Fe3+ system