Cycloaddition Chemistry of 2-Vinyl-Substituted Indoles and Related Heteroaromatic Systems
作者:Albert Padwa、Stephen M. Lynch、José M. Mejía-Oneto、Hongjun Zhang
DOI:10.1021/jo047834a
日期:2005.3.1
The intramolecular Diels−Alder cycloaddition reaction (IMDAF) of several N-phenylsulfonylindolyl-substituted furanyl carbamates containing a tethered π-bond on the indole ring were examined as an approach to the iboga alkaloid catharanthine. Only in the case where the tethered π-bond contained two carbomethoxy groups did the [4 + 2]-cycloaddition occur. Push−pull dipoles generated from the Rh(II)-catalyzed
Vicarious nucleophilic substitution of hydrogen versus vinylic substitution of halogen in the reactions of carbanions of halomethyl aryl sulfones with dialkyl halofumarates and halomaleates
halomethyl aryl sulfone carbanions with dialkyl halofumarates and halomaleates results in nucleophilicsubstitution of hydrogen and/or of the halogen. The reaction with halofumarates proceeds via addition of the carbanions to the vinylic carbon atom connected with hydrogen, followed by base promoted β-elimination of hydrogen halide in which the halogen originates from the carbanion moiety or from the alkene
Reduction D′α,α′-dibromoorthoxylenes par les sels chromeux : generation facile d'orthoquino-dimethanes
作者:D. Stephan、A. Gorgues、A. Le Coq
DOI:10.1016/s0040-4039(01)91403-0
日期:1984.1
α,α′-Dibromoorthoxylenes undergo a very fast reductive elimination on treatment with chromouschloride, affording the reactive intermediate orthoquinodimethanes which evolve into spiroorthoxylylenes 2 or may be trapped with dienophiles (adducts 3 and 4). Some attempts in the field of anthracycline precursors are reported.
Bis-esters from maleic anhydrides under neutral conditions: Protection of the anhydride of the natural product cornexistin
作者:Stephen C. Fields、William H. Dent、F.Richard Green、Eric G. Tromiczak
DOI:10.1016/0040-4039(96)00182-7
日期:1996.3
Trimethylsilyldiazomethane converts maleic anhydride derivatives in alcoholic THF to bisesters. The highly acid and base sensitive natural product cornexistin was converted to its bis-methyl ester in 70–75% yield and to the mixed benzyl/methyl ester in 61% yield. The mixed ester can be converted back to cornexistin via transfer hydrogenation.
A process for producing a dicarboxylic acid compound represented by the formula (4):
wherein R
1
and R
2
are the same or different and each represents lower alkyl and the wavy line indicates that this compound is the E- or Z-isomer or a mixture of them, characterized by reacting a compound represented by the formula (2):
wherein R
1
, R
2
and the wavy line have the same meanings as the above, and one of X
2
and X
3
represents hydrogen and the other represents halogen, with nitrophenol represented by the formula (3):
in the presence of a base; a process for producing a nitrochromone compound represented by the formula (5):
wherein R
1
has the same meaning as the above, characterized by reacting the dicarboxylic acid compound or carboxylic acid thereof with an acid; a process for producing an aminochromone compound which comprises reducing the nitrochromone compound; and a process for producing an amidochromone compound which comprises acylating the aminochromone compound are provided.