Transition Metal‐Diene Complexes in Organic Synthesis. Part 15. Iron‐mediated total synthesis of carbazomycin A and B

Abstract

We developed a very efficient methodology for the synthesis of the antibiotics carbazomycin A (1) and B (2) by oxidative coupling of cyclohexa-1,3-diene and the corresponding arylamine 10 (Scheme 5 and Schemes 7 and Y, resp.). The overall process is achieved by a consecutive Fe-induced formation of the C-C and the C-N bond. The major benefit of our Fe-mediated carbazole synthesis is that the coupling process is possible with fully functionalized arylamines 10. Therefore, highly convergent syntheses of carbazole alkaloids are feasible, and linear multistep sequences as required by using classical procedures are avoided. The total synthesis of 1 and 2 emphasizes this characteristic feature of the Fe-mediated construction of the carbazole framework.

Efficient and Green Telescoped Process to 2-Methoxy-3-methyl-[1,4]benzoquinone

“…Nitric acid as the acid catalyst affords the needed intermediate product 13 , although only in a very low quantity. The major product was the phenol 12 , − which, however, is another important phenolic compound that can be used in the synthesis of various biologically active compounds, such as the antibiotics carbazomycine B and C 25 and 4,5-diacyloxybenzofurans, which are valuable leukotriene inhibitors 2 Oxidation of 11 with Various Acid Catalysts Present a entrycat.…”

Isolation and Synthesis of Biologically Active Carbazole Alkaloids

“…After deacetylation the corresponding phenol, 274b was methylated and subjected to hydrogenation to give the arylamine 270a . This synthesis provided the arylamine 270a in eight steps and 31% overall yield (Scheme ). ,,

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“…Oxidative cyclization of complex 275a in toluene at room temperature with very active manganese dioxide afforded carbazomycin A ( 261 ) in 25% yield along with the tricarbonyliron-complexed 4b,8a-dihydro-3 H -carbazol-3-one 276 (17% yield). The quinone imine 276 was also converted to carbazomycin A ( 261 ) by a sequence of demetalation and O -methylation (Scheme ). , The synthesis via the iron-mediated arylamine cyclization provides carbazomycin A ( 261 ) in two steps and 21% overall yield based on 12a .

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Planar Chiral Cp*Ru Complexes. 2.1Bis(allyl) and -(arene) Complexes Derived from (R)-Carvone

“…This is due to the highly stereospecific elaborations possible in π-ligand systems complexed to transition metal fragments. Diastereospecific metalation of substituted ferrocenesand arene tricarbonyl Cr complexes as well as carbon−carbon bond forming reactions at cationic dienyl−Fe(CO) 3 and arene tricarbonyl Cr complexes are intensively studied examples. In cases where the π-ligand is prochiral, planar chirality is generated in the complexation reaction and any successive stereospecific elaborations will lead to enantiomerically pure compounds, only to the extent to which the enantiomeric purity of the starting π-complex can be ascertained.…”