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

Dedicated to Prof. Dieter Seebach on the occasion of his 60th birthday (1 3.11.97) The [Rh,(OAc),]-catalyzed decomposition of {[(4-nitrophenyl)sulfonyl]imino}phenyl-13-iodane (NsN=IPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by 0-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 Rh" catalysts, a modest asymmetric induction was observed. A mechanism involving direct insertion by a Rh-complexed nitrene into the CH bond is proposed.

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Two cis-fused cyclopenteno-1,2,4-trioxanes, l a and lb, were subjected lo Zn in AcOH or FeCl,.4H20 in MeCN. In the first case, the main course was deoxygenation to give cyclopentanone (18) and the 1,Cdiphenyl-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-hydrcxycyclopent-2-enyl 5-hydroxypentanoates 8 (Scheme 3 ) .

The aziridination of olefins with {(4-nitrophenylsulfonyl)imino}phenyl-λ 3 -iodane, NsNTIPh (1c), in the presence of [Rh 2 (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 ρ-value for aziridination of substituted styrenes is -0.61. No ring-opened products are observed upon aziridination of vinylcyclopropanes. In the presence of chiral Rh II catalysts, the aziridination is enantioselective, affording an ee of 73% with cis-β-methylstyrene (4k) and Pirrungs [Rh 2 {(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.

Reaction of 1H-cyclopropa[b]naphthalene ( l a ) or 1H-cyclopropa [b]anthracene (10a) with tris(acetonitri1e)tricarbonylchromium affords cyclobutanaphthalenone and cyclobutaanthracenone 2 and 11, respectively. In contrast, the bis-silylated cycloproparenes l b and 10b undergo complexation at the terminal benzene ring and lead to the arene-tricarbonylchromium complexes 4b and 12, respectively. Desilylation of 4b to 4a is effected by t-BuOK.

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