A new synthesis of 4- and 7-carbon-substituted indoles is described. The overall sequence involves the addition of a nitrile oxide to 1 carboethoxy-2-(or 3-) allylpyrrole, hydrogenation of the intermediate isoxazoline to β-hydroxy ketone and cyclization of the ketol using magnesium or zinc triflate to the substituted indole. This new indole-forming strategy can also accommodate the introduction of oxygen functionality into the indole 6-position. Possible mechanistic aspects of the reaction are detailed. 相似文献
Prenylated indole alkaloids derived from L ‐tryptophan are widely distributed in nature and show diverse biological and pharmacological activities, usually distinct from their non‐prenylated precursors. Prenyltransferases catalyze the transfer reactions of prenyl moieties onto the indole nucleus and contribute largely to the structural diversity of these compounds. In this study, we demonstrate the acceptance of cyclo‐L ‐homotryptophan‐D ‐valine, an unnatural cyclic dipeptide, by eight prenyltransferases of the dimethylallyltryptophan synthase superfamily. Seven products with one prenyl moiety at each position of the indole nucleus and one diprenylated derivative were isolated from enzyme assays of cyclo‐L ‐homotryptophan‐D ‐valine with dimethylallyl diphosphate. To the best of our knowledge, this is the first report for production of seven monoprenylated products from one substrate by one‐step reactions.
Communesins A–H are a growing family of natural products isolated from a marine fungal strain of Penicillium species. Preliminary biological evaluation has revealed that these compounds possess insecticidal activity and cytotoxicity against several tumor cell lines. Their interesting biological activities and unique structures have attracted considerable attention of synthetic chemists worldwide. To date, several elegant protocols for assembling the core structure of these indole alkaloids have been described, including intermolecular Diels–Alder reaction of methylated aurantioclavine with quinine methide imine and intramolecular hetero Diels–Alder reaction of the azaortho-xylylene intermediates. Recently, three completed total syntheses for communesin F have been disclosed, in which the crucial vicinal quaternary stereogenic centers were constructed by employing an intramolecular cyclopropanation; an intramolecular Heck reaction of a tetrasubstituted alkene, or an oxidative coupling of a 3-substituted indole, as the key step. Accompanying the total synthesis, the absolute configuration of natural communesin F was established as 6R,7R,8R,9S,11R. However, total syntheses of other members of communesin family that contain an epoxide moiety have not been achieved, which will stimulate more synthetic studies. 相似文献
Chemodivergent and stereoselective construction of indole‐containing scaffolds, as well as synthesis of diverse indole derivatives, has long been a goal in the chemistry community. In this work, we reveal key intermediate‐dependent unusual [4+3], [3+2] and cascade reactions of 3‐indolylmethanols with Nazarov reagents, leading to controllable chemodivergent and stereoselective synthesis of diverse indole derivatives. (i) In the presence of hydrobromic acid in acetonitrile, 3‐indolylmethanols performed an electronically reversed [4+3] cyclization with Nazarov reagents, thus constructing a cyclohepta[b]indole framework with the concomitant creation of an all‐carbon seven‐membered ring bearing a quaternary stereocenter in a highly diastereoselective fashion. (ii) Under the promotion of hydrobromic acid in fluorobenzene, methyl‐protected 3‐indolylmethanols underwent site‐selective [3+2] cyclization with Nazarov reagents, which built up a cyclopenta[b]indole skeleton bearing a spiro‐quaternary stereocenter in high chemical yields. (iii) By changing the acid to trifluoromethanesulfonic acid in acetonitrile, the same reactants carried out a cascade reaction to afford the corresponding indole derivatives by generating multiple new C C bonds in an (E/Z)‐selective mode. Based on control experiments, these reactions were found to be dependent on the formation of a key type of intermediate, which underwent a variety of unusual transformations including C C bond cleavage and reassembly under different reaction conditions to afford diverse indole derivatives. These unusual reactions not only for the first time establish several challenging new transformations of 3‐indolylmethanols with precise control of chemo‐, diastereo‐ and (E/Z)‐selectivity, but also provide efficient methods for constructing indole‐containing scaffolds in a stereoselective and chemodivergent manner.
Intramolecular oxidative palladium‐catalyzed reactions of indolylallylamides in the presence of the couple bis(acetonitrile) palladium dichloride and copper(II) halide are described. Starting from 2‐ and 3‐indolylallylamides and involving in both cases the C‐3 position of the indole nucleus, variously substituted β‐carbolinones were obtained by arylation/halogenation, arylation/esterification or arylation/carboalkoxylation processes. On the other hand, an unusual aminohalogenation/halogenation sequence performed on 2‐indolylallylamides gave rise to pyrazino[1,2‐a]indole products. The carboesterification process is the result of an unknown path that involves the DMF or DMA used as solvent. The outcome of the reactions of the 3‐indolylallylamides arises from a totally selective 1,2‐migration of the acyl group on the supposed spiro intermediates formed from the nucleophilic attack of the C‐3 indole position. 相似文献
Cycloaddition Elimination Reactions of 4-Aryl-5-arylimino-1,2,4-dithiazolidin-3-ones (Mustard Oil Oxides) 4-Aryl-5-arylimino-1,2,4-dithiazolidin-3-ones ( 1 ) react with isocyanates, isothiocyanates, and cyanic acid esters by exchange of the COS-part from 1 affording thiadiazole and dithiazole derivatives 4 , 5 , 6 or 12 . The reaction products are able to give further exchange reactions. Ring opening of 2-substituted 4-aryl-5-arylimino-1,2,4-thiadiazolin-3-ones ( 4 ) and -3-thiones ( 6 ) yields thio- and dithiobiurets ( 7 , 8 ) with aryl substituent in 3-position. Oxidation of dithiobiurets, generated from 6 , affords dithiazolidines 9 , which are Dimroth-isomers of 6 . 相似文献
