Transition metals in organic synthesis. Part 108: first total synthesis of ekeberginine

Using a palladium(II)-catalyzed oxidative cyclization and a regioselective nickel-mediated prenylation as key steps, the first total synthesis of the 1-oxygenated carbazole alkaloid ekeberginine has been achieved in six steps and in 63% overall yield.     

Transition metal-diene complexes in organic synthesis - 16. : Iron-mediated total synthesis of 1-oxygenated carbazole alkaloids

Using a methodology of consecutive iron-induced C---C and C---N bond formation we describe the total synthesis of murrayafoline A, murrayaquinone A, koenoline, murrayanine, mukoeic acid, and mukonine.     

Total synthesis of carbazole alkaloids

A Suzuki-Miyaura cross coupling, followed by triphenylphosphine mediated Cadogan reductive cyclization sequence provided efficient access to a series of carbazole alkaloids.In the present work, this approach was applied to the total synthesis of mukonine, clauszoline K, koenoline, murrayanine, murrayafoline A, mukoeic acid, glycoborine, glycozolicine, mukolidine, mukoline, glycozoline, 3-methoxy-9H-carbazole-1-carboxylic acid methyl ester, (3-methoxy-9H-carbazol-1-yl)-methanol, 3-methoxy-9H-carbazole-1-carbaldehyde, 3-methoxy-9H-carbazole-1-carboxylic acid, 2-methyl-9H-carbazole and nonsteroidal anti-inflammatory drug (NSAID) carprofen and its derivatives.     

Transition metals in organic synthesis: highlights for the year 1999

A review with 1621 references to transition metal catalyzed or mediated carbon–carbon bond forming reactions and functional group preparations.     

First total synthesis of the biologically active 2,7-dioxygenated tricyclic carbazole alkaloids 7-methoxy-O-methylmukonal, clausine H (clauszoline-C), clausine K (clauszoline-J) and clausine O

Using the iron-mediated arylamine cyclization as the key step we have achieved a short and highly efficient access to the biologically active 2,7-dioxygenated tricyclic carbazole alkaloids 7-methoxy-O-methylmukonal, clausine H (clauszoline-C), clausine K (clauszoline-J) and clausine O.     

Tellurium/lithium exchange reactions in the synthesis of spiroketals and 1,6-dioxygenated systems

1,4-C,O-dianions have been generated through concomitant acid/base and tellurium/lithium exchange reactions. The di-lithium salts were transmetallated with cerium chloride to the corresponding di-cerium salts and subsequently reacted with lactones and carboxylic acid anhydrides to yield the respective spiroketals. The di-lithium entities were also converted into the corresponding cyanocuprates that add in a 1,4-manner to 2-cyclohexen-1-one to form 1,6-dioxygenated compounds.     

Convergent total synthesis of squamostolide

A convergent total synthesis of the Annonaceous acetogenin squamostolide, in a longest linear sequence of nine steps from d-mannitol, is reported. Central to the efficiency of the synthesis is a highly selective tandem ring-closing/cross metathesis step in which lactone formation and fragment coupling are accomplished.     

Transition metal complexes in organic synthesis. Part 68: Iron-mediated total synthesis of mukonine and mukonidine by oxidative cyclization with air as the oxidizing agent

The oxidative cyclization of 5-(2-amino-5-methoxycarbonylphenyl)-substituted tricarbonyl[η⁴-cyclohexa-1,3-diene]iron complexes by air in protic medium provides the corresponding tricarbonyl[η⁴-4a,9a-dihydro-9H-carbazole]iron complexes. This procedure is applied to the total synthesis of the 3-methoxycarbonylcarbazole alkaloids mukonine and mukonidine.     

Convergent approach to pumiliotoxin alkaloids. Asymmetric total synthesis of (+)-pumiliotoxins A,B, and 225F

A versatile convergent approach for preparing the pumiliotoxin alkaloids has been developed employing Pd(0)-catalyzed cross-coupling reactions between homoallylic organozincs and vinyl iodides. The (Z)-iodoalkylidene indolizidine 34, which served as a common key intermediate, was synthesized through highly stereoselective addition of the chiral silylallene 19 to (S)-acetylpyrrolidine followed by a palladium-catalyzed intramolecular carbonylation[bond]cyclization sequence. This synthetic process allowed the first total synthesis of (+)-pumiliotoxin 225F. The intermediate (Z)-iodoalkylidene indolizidine 34 obtained was converted to a homoallylzinc chloride derivative and subjected to homoallyl-vinyl cross-coupling with the (E)-vinyl iodide 42 using Pd(PPh(3))(4) catalyst to give the cross-coupled product 47 with a 1,5-diene side chain. Subsequent deprotection provided (+)-pumiliotoxin A. On the other hand, the (Z)-iodoalkylidene indolizidine 34 was transformed into the homoallyl-tert-butyl zinc derivative, which underwent palladium-catalyzed cross-coupling with the (E)-vinyl iodide 50 and subsequent deprotection to afford (+)-pumiliotoxin B.     

Convergent total synthesis of (+)-mycalamide A

The details of a convergent total synthesis of (+)-mycalamide A are described. Yb(OTf)3-TMSCl-catalyzed cross-aldol reaction conditions are used to synthesize the right segment of mycalamide A. In this reaction, an acid-sensitive aldehyde reacts with methyl trimethylsilyl dimethylketene acetal without epimerization to provide the desired aldol adduct. Additionally, a tetrahydropyran ring, which is the left segment of mycalamide A, is prepared using a novel one-pot delta-lactone formation methodology. Both segments are constructed from a common starting material, d-mannitol. These segments are then coupled in the presence of BuLi, and the functional groups are transformed to complete the synthesis of (+)-mycalamide A.     

Transition metal mediated organic synthesis: The synthesis of moracin M.

The Palladium catalysed cross coupling of 2-halo- or metallo-benzofurans with both 5-metallo- or halo-resorcinol tricarbonyl chromium(O) complexes and the uncomplexed resorcinols, has been evaluated and in consequence, moracin M has been synthesised in good yield by the cross coupling of 6-(t-butyldiphenylsiloxy)-2-trimethylstannylbenzofuran with 5-iodoresorcinolbis(triisopropylsilyl) ether and fluoride ion deprotection of the product.     

Short synthesis of carbazole alkaloids: Ekeberginine,murrayaquinone A,and glycozoline

Three differently substituted, naturally occurring, biologically active carbazole derivatives (viz. ekeberginine, murrayaquinone A, and glycozoline) were synthesized in good yield using short and simple routes. The prenyl group was selectively introduced at the C4 position using a Stille coupling reaction in the synthesis of ekeberginine. Murrayaquinone A was synthesized using Raney nickel–mediated desulfurization of dithiane as a key step. Synthesis of glycozoline was achieved in two steps from 3-methyl carbazole via an intermediate 3-bromo-6-methyl carbazole.     

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

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 9, 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.     

Transition metal-catalyzed cyclocarbonylation in organic synthesis

Cyclocarbonylation reactions proceed mainly by the coupling reactions of carbonylation components with cyclization components having an unsaturated π-electron bond, in the presence of transition metal compounds. The representative reactions are cyclocarbonylation of alkynes by carbon monoxide such as Pauson–Khand reactions, hetero Pauson–Khand reactions, cyclocarbonylation of alkynyl alcohols, cyclocarbonylation of alkynyl amines, cyclocarbonylative alkyne–alkyne coupling reactions, and reductive cyclocarbonylation of alkynes. The other reactions are cyclocarbonylation of alkenes by carbon monoxide such as alkene–alkene coupling reactions, cyclocarbonylation with aldehydes, ketones, amines or imines, cyclocarbonylation of alkenyl alcohols. Carbonylation via cyclometalation, carbonylative ring expansion reactions, cyclocarbonylation by aldehydes, carboxylic acids or carboxylic acid esters are also cyclocarbonylation reactions. These reactions are conveniently used for organic syntheses, especially, for the syntheses of pharmaceutical intermediates.