HETEROCYCLES

■ Contents

■ Honoring the 77th Birthday of Professor Ei-ichi Negishi

Robert M. Williams*

*Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, U.S.A.

■ CONGRATULATIONS TO PROFESSOR EI-ICHI NEGISHI ON His KI-JU (77TH BIRTHDAY)

Takumichi Sugihara*

*Department of Pharmacy, Niigata University of Pharmacy and Applied Life Sciences, 265-1, Higashi-jima, Akiha-ku, Niigata 956-8603, Japan

■ Short Biographical Sketch - Ei-ichi Negishi

Ei-ichi Negishi*

*Wetherill Laboratory, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, U.S.A.

■ LIST OF PUBLICATIONS BY EI-ICHI NEGISHI

Ei-ichi Negishi*

*Wetherill Laboratory, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, U.S.A.

■ Surveying the Effects of Eldecalcitol and Related Analogs from a Biological Perspective

Noboru Kubodera*

*International Institute of Active Vitamin D Analogs, 35-6, Sankeidai, Mishima, Shizuoka 411-0017, Japan

Abstract

In the previous review paper, explorative and developmental researches of eldecalcitol (1α,25-dihydroxy-2β-(3-hydroxypropoxy)vitamin D3), an analog of active vitamin D3, calcitriol (1α,25-dihydroxyvitamin D3), were introduced. Eldecalcitol possesses potent effects on bone disease such as osteoporosis. The completion of a phase III clinical trial of eldecalcitol for bone fracture prevention in comparison with alfacalcidol (1α-hydroxyvitamin D3), prodrug of calcitriol, produced excellent results. Although clinically, eldecalcitol showed greater potency than calcitriol/alfacalcidol, the detailed physiological properties and mechanism of action of the enhanced activity of eldecalcitol toward bone remains to be clarified. To explore structure-activity relationships, related analogs of eldecalcitol have been synthesized with inherent biological background of each targeted analogs. These include epimeric analogs at 1, 2, 3, and 20 positions, nor analog at 19 position and deoxy analogs at 1 and 25 positions. This review discusses eldecalcitol and related analogs in a biological perspective. The synthetic features of analogs are also outlined.

■ Synthesis of Two Neurokinin NK1 Receptor Antagonists: (+)-L-733,060 and (-)-L-733,061

Anne Cochi, Domingo Gomez Pardo, and Janine Cossy*

*Laboratoire de Chimie Organique, ESPCI, 10, rue Vauquelin
75231 PARIS Cedex 05, France

Abstract

This review describes synthetic approaches to (+)-L-733,060 and (–)-L-733,061 reported since 1994, focusing on methods allowing the construction and control of the two stereogenic centers. The methods are divided into three groups: (1) resolution of racemates (chemical or enzymatic resolution), (2) diastereoselective reactions using chiral pools or auxiliaries, and (3) enantioselective reactions (aminohydroxylation, epoxidation, deprotonation, allylic amination, aza-Henry reaction, vinylogous aldolization).

■ SULFUR- AND N-ACYL CARBONYL OXYGEN-ASSISTED HETEROLYSIS OF THE C(=O)–S BOND IN EXCITED-STATE (Z)-N-ACYL-α-DEHYDRO(1-NAPHTHYL)ALANINE THIOESTERS

Yosuke Hosoi, Tetsutaro Igarashi, and Tadamitsu Sakurai*

*Department of Material and Life Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan

Abstract

Irradiation of the title thioesters (Z)-1 in nitrogen-saturated 1,2-dichloroethane at wavelengths greater than 280 nm was found to afford (Z)-4-(1-naphthylmethylene)-5(4H)-oxazolone derivatives (Z)-2, (E)-2, alkyl-substituted thiols 3, and (E)-1 without forming any thio-radical-derived products. An analysis of the substituent and solvent effects on the reactivity of 1 and the product distribution demonstrated that the heterolytic C(=O)–S bond cleavage products 2 and 3 are not derived from the long-lived acylium and thiolate ions but from the protonated oxazolone/thiolate ion pair. The latter intermediates were assumed to be formed by the sulfur-assisted nucleophilic addition of the N-acyl carbonyl oxygen to the thioester carbonyl carbon in the excited state, followed by the elimination of the thiolate ion from the resulting adducts.

■ A CONCISE SYNTHESIS OF THE AB-RING FRAGMENT OF (−)-GAMBIEROL

Haruhiko Fuwa,* Kazuaki Hirota, and Makoto Sasaki*

*Graduate School of Life Sciences, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan

Abstract

We describe herein a concise synthesis of the AB-ring fragment of gambierol, wherein silver(I) trifluoromethanesulfonate-catalyzed 6-endo cyclization of a hydroxy ynone was exploited for the formation of the A-ring.

■ Nickel-Catalyzed Borylation of Aryl Halides with 4,4,6-Trimethyl-1,3,2-dioxaborinane

Miki Murata,* Yosuke Sogabe, Takeshi Namikoshi, and Shinji Watanabe

*Department of Materials Science and Engineering, Kitami Institute of Technology, Koen-cho 165, Kitami, Hokkaido 090-8507, Japan

Abstract

The nickel-catalyzed borylation of aryl iodides and bromides with 4,4,6-trimethyl-1,3,2-dioxaborinane was achieved. The mild reaction conditions employed allowed for the inclusion of common functional groups in aryl halides to be tolerated. A DFT study on the catalytic cycle shows that C–B bond formation occurs through σ-bond metathesis between dialkoxyborane and arylnickel(II) halide intermediates.

■ DESIGN AND SYNTHESIS OF A C2-SYMMETRIC CHIRAl 1,2-BIS(DIPHENYLPHOSPHINO)BENZENE LIGAND VIA RHODIUM-CATALYZED INTRAMOLECULAR [2+2+2] CYCLOADDITION

Fumiya Mori, Keiichi Noguchi, and Ken Tanaka*

*Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo184-8588, Japan

Abstract

The design and synthesis of a C2-symmetric chiral 1,2-bis(diphenylphosphino)benzene ligand via the rhodium-catalyzed intramolecular [2+2+2] cycloaddition followed by reduction are disclosed. This new chiral dppbz-type ligand could be employed for the rhodium-catalyzed asymmetric alkene hydrogenation.

■ Construction of All-Carbon Quaternary Stereocenters by Zinc-Mediated Barbier-Type Allylation in Aqueous Media

Ken-ichi Takao,* Tomo Miyashita, Nozomi Akiyama, Takuya Kurisu, Kohei Tsunoda, and Kin-ichi Tadano*

*Department of Applied Chemistry, Faculty of Science and Technology, Keio University, Hiyoshi, Kohoku-ku Yokohama 223-8522, Japan

Abstract

Stereoselective synthesis of all-carbon quaternary stereocenters by Barbier-type allylation in aqueous media is described. Sugar-derived aldehydes, 2,3-O-isopropylidene-D-glyceraldehyde and 2,4-O-benzylidene-D-threose, were reacted with geranyl chloride in the presence of zinc powder to provide γ-adducts bearing quaternary stereocenters with good stereoselectivity.

■ STEREOSELECTIVE SYNTHESIS OF THE FUSED γ-LACTONE/δ-LACTONE CORE OF OPHIODILACTONES

Takaaki Matsubara, Keisuke Takahashi, Jun Ishihara, and Susumi Hatakeyama*

*Graduate School of Biomedical Sciences, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

A promising precursor of ophiodilactones A and B, tetrameric phenyl propanoids isolated form the ophiuroid Ophiocoma scolopendrina, has been synthesized stereoselectively employing a halolactonization and an intramolecular epoxide-opening with a carboxylic acid as key reactions.

■ SYNTHESIS OF p-CHLOROAZACALIX[5]ARENE PENTAMETHYL ETHER: RING SIZE-DEPENDENT DEPROTECTION OF N-BENZYL GROUPS

Hirohito Tsue,* Kazuyuki Miyata, Daisuke Takahashi, Hiroki Takahashi, Kohei Sasaki, and Rui Tamura

*Department of Interdisciplinary Environment, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 606-8501, Japan

Abstract

Syntheses of chlorinated azacalix[4]arene and azacalix[5]arene have been investigated. While the preparation of the former failed in the final N-debenzylation step, the latter was successfully obtained. The observed ring size-dependent deprotection was interpreted by steric effect.

■ FACILE SYNTHESIS AND ESTROGENIC ACTIVITY OF ARYLPYRROLE-BASED BISPHENOL DERIVATIVES

Kiminori Ohta, Fumi Taguchi, and Yasuyuki Endo*

*Faculty of Pharmaceutical Sciences, Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai 981-8558, Japan

Abstract

Novel estrogen candidates 6a and 6b incorporating arylpyrrole bisphenol structure were efficiently synthesized in three steps from commercially available materials by means of McMurry coupling and an unexpected BBr3-mediated aromatization. These compounds showed ERα-binding affinity in competitive binding assay and estrogenic activity in MCF-7 cell proliferation assay.

■ Palladium-CATALYZED TANDEM COUPLING REACTION OF ALKYNE, CONJUGATED DIENE, AND TRIETHYLBORANE

Daiki Takushima, Masahiro Fukushima, Hideaki Satomura, Gen Onodera, and Masanari Kimura*

*Division of Chemistry and Materials Science, Graduate School of Engineering, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

Pd(0) catalyst promotes three-component coupling reactions of allylic alcohols and vinylcyclopropanes with terminal alkynes and triethylborane to provide (E)-1-substituted 2-ethyl-1,4-pentadienes and (E)-1-substituted 2-ethyl-1,4-heptadienes involving geminal ethylation and allylation at the acetylenic terminal carbon atom with high regio- and stereoselectivities. 1,3-Butadiene and bis-dienes can act as allylating agents to undergo the multi-component coupling reactions, accompanied by dimerization of the diene moieties, to provide 1,4,9-decatrienes and pyrrolidines with excellent regio- and stereoselectivities.

■ Selective Introduction of Four Contiguous Stereocenters on the B-Ring of 4-Hydroxyzinowol

Masafumi Iwatsu, Daisuke Urabe, Hidenori Todoroki, Kengo Masuda, and Masayuki Inoue*

*Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Abstract

4-Hydoxyzinowol is a bioactive polyoxygenated dihydro-β-agarofuran sesquiterpenoid. Here we describe construction of four contiguous cis-oriented stereocenters on the B-ring of 4-hydroxyzinowol. Introduction of a C7-isopropenyl group by the 1,4-addition of isopropenyl magnesium bromide was effectively assisted by methyl aluminum bis(2,6-di-tert-butyl-4-methylphenoxide). Taking advantage of the presence of the C7-substituent, three hydroxy groups were installed in a stereoselective fashion at the C6, 8 and 9 positions. In this study, we employed a new reagent combination of Sc(OTf)3 and Zn(OTf)2 for the hydrolysis of the cyclic acetal on the rigid oxabicyclo[3.2.1]octane structure.

■ A Diversified Approach to the Synthesis of Highly Functionalized Novel Azines and Azoles from 2H-Pyran-2-ones

Pushyamitra Mishra, Sandeep Kumar, Hardesh K. Maurya, Sanjay K. Gautam, Brijesh Kumar, Vishnu K. Tandon,* and Vishnu Ji Ram*

*Department of Chemistry, University of Lucknow, Lucknow, U.P. 226007, India

Abstract

One-pot regioselective synthesis of 2,6-diarylpyrimidines (4), 2,6-disubstituted pyridines (5 and 6), 5-aryl-3-cyanomethyl-1H-pyrazoles (7) through base catalyzed ring transformation of suitably functionalized 2H-pyran-2-ones by arylamidines, cyanamide, ammonium carbonate, hydrazines respectively has been developed. Our synthetic approach opened a new avenue for the regioselective synthesis of 2,6-diarylpyrimidines and 2,6-disubstituted pyridines and cyanomethylpyrazoles. The procedure is very simple, efficient and economically viable. The protocol provides an efficient methodology for the preparation of new class of medicinally useful and highly functionalized azines and azoles from single precursor 2H-pyran-2-ones.

■ Highly Enantioselective Synthesis of Isoquinuclidine by Diels-Alder Reaction of 1,2-Dihydropyridine Utilizing Chiral Bisoxazoline-Cu(II) Complex

N. D. M. Romauli Hutabarat, Chigusa Seki,* Takashi Shimizu, Masafumi Hirama, Yoshihito Kohari, Hiroto Nakano, Koji Uwai, Nobuhiro Takano, Eunsang Kwon, and Haruo Matsuyama*

*Department of Applied Chemistry, Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran, Hokkaido 050-8585, Japan

Abstract

The enantioselective Diels-Alder (D-A) reaction between N-phenoxycarbonyl- or N-benzyloxycarbonyl-1,2-dihydropyridine (1a or 1b) and N(2)-acryloyl-N(1)-(1-naphthylmethyl)-5,5-dimethylpyrazolidin-3-one (2b) using (S,S)-bisoxazoline-Cu(II) catalyst (A, B, C or D) has been investigated. Utilizing (S,S)-t-Bu-bisoxazoline-Cu(II) catalyst C, the D-A reaction of 1a and 2 afforded the endo-(7S)-isoquinuclidines (3, 4 or 5) in good chemical yields with high enantioselectivity (up to 99% e.e.).

■ Formal Synthesis of Hapalindole O and Synthetic Efforts towards Hapalindole K and Ambiguine A

Ryan J. Rafferty and Robert M. Williams*

*Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, U.S.A.

Abstract

he formal synthesis of D,L-hapalindole O has been accomplished intercepting Natsume’s total synthesis route. The intercepted substrate was synthesized in an overall 36% yield over ten-synthetic steps compared to Natsume’s overall 1% yield over eighteen-synthetic steps. In addition, advanced substrates for the continuing progress towards hapalindole K and ambiguine A has been synthesized. All routes described herein employ a silyl ether-based strategy accessing the functionalized 6:5:6:6 ring system, that has previously been used in our laboratory to access the total synthesis of D,L-hapalindoles J and U.

■ Synthesis, Cyclization, and Evaluation of the Anticancer Activity against HeLa S-3 Cells of Ethyl 2-Acetylamino-3-ethynylazulene-1-carboxylates

Marie Hyoudou, Hajime Nakagawa, Takahiro Gunji, Yoshino Ito, Yu Kawai, Reiko Ikeda, Takeo Konakahara, and Noritaka Abe*

*Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan

Abstract

Reaction of ethyl 2-aminoazulene-1-carboxylate with NIS in CHCl3 gave 2,2’-diamino-3,3’-diethoxycarbonyl-1,1’-biazulene (3) and a terazulene derivative. The coupling of azulenes was catalyzed by acid. Operation of the reaction in the presence of Et3N in CH2Cl2 for 7 min at -7 °C retarded the coupling of the azulene nuclei to give ethyl 2-amino-3-iodoazulene-1-carboxylate (1a) in 95% yield. Sonogashira cross-coupling of ethyl 2-acetylamino-3-iodoazulene-1-carboxylate (1b) gave ethyl 2-acetylamino-3-ethynylazulene-1-carboxylates (5a and 5b) in good yields. Cyclization of ethyl 2-acetylamino-3-phenylethynylazulene-1-carboxylate with Pd-catalyst gave azuleno[2,1-b]pyrrole derivatives. Compounds (3 and 5b) showed potent cytotoxic activity against HeLa S-3 cells (IC50 [μM] : 3: 2.9 ± 0.2, 5b: 13.4 ± 1.1).

■ Antimalarial Spiro-Bridged 1,2-Dioxolanes via Intramolecular Addition of Peroxycarbenium Ions to C-C Double Bonds

Yun Li, Sergio Wittlin, and Yikang Wu*

*State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, 345 Lingling Road, Shanghai 200032, China

Abstract

Several 1,2-dioxolanes embedded in a rigid spiro-bridge framework fused with a built-in UV chromophore were synthesized through intramolecular [3+2] addition of in situ generated peroxycarbenium ions to C-C double bonds.

■ C-H Arylation of 3-Substituted Thiophene with Regioselective Deprotonation by TMPMgCl·LiCl and Transition Metal Catalyzed Cross Coupling

Shota Tanaka, Shunsuke Tamba, Atsushi Sugie, and Atsunori Mori*

*Department of Chemical Science and Engineering, Faculty of Engineering, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan

Abstract

The reaction of 3-hexylthiophene with Knochel-Hauser base (TMPMgCl⋅LiCl) induced the metalation at the 5-position of the thiophene ring selectively. Following addition of several aryl halides in the presence of a nickel or palladium catalyst afforded regioselectively arylated thiophene in good to excellent yields.

■ Reissert-like Alkenylation of Azaaromatic Compounds with Alkenylzirconocene Chloride Complexes

Akio Saito,* Kohei Sudo, Koichi Iimura, Miki Hayashi, and Yuji Hanzawa*

*Showa College of Pharmaceutical Sciences, 3-3165, Higashi-tamagawagakuen, Machida, Tokyo 194-8543, Japan

Abstract

Reissert-like alkenylation of azaaromatic compounds by the use of alkenylzirconocene chloride as a nucleophile was carried out in the presence of a stoichiometric amount of ClCO2Et. The regioselectivity of the nucleophilic attack depends on reacting heterocycles, solvent, and the presence of copper catalyst. Thus, the reaction of quinoline derivatives with alkenylzirconocene chloride in MeNO2 proceeded in a preferential 1,2-addition manner to give N-ethoxycarbonyl-2-alkenyl-1,2-dihydroquinolines, and the reaction of pyridine in CH2Cl2 under Cu(I)-catalyzed conditions proceeded in a 1,4-addition manner to give N-ethoxycarbonyl-4-alkenyl-1,4-dihydropyridine. The alkenylation of 3,4 -dihydroisoquinoline with alkenylzirconocene chloride was also carried out in an enantioselective manner under Cu(I)/chiral Box-catalyzed conditions to give alkenylated tetrahydroisoquinoline compound (75%ee).

■ Synthesis of Antineoplastic Analogs of Aplysiatoxin with Various Side Chain Structures

Yuki Shu, Ryo C. Yanagita, Harukuni Tokuda, Nobutaka Suzuki, and Kazuhiro Irie*

*Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan

Abstract

We have recently developed a simplified analog of aplysiatoxin with anti-proliferative activity (1). To investigate the structure–activity relationship of its side chain, an alternative synthetic route of 1 has been established. Via the key intermediate 6, p-hydroxyl or o,m-dihydroxyl derivatives (4 and 5) as well as 1 were synthesized and their biological activities were evaluated. Although the position of the hydroxyl group in the benzene ring did not change the affinity for protein kinase C isozymes or the ability to induce the Epstein-Barr virus early antigen, anti-proliferative activities against several human cancer cell lines of 1 were superior to those of 4.

■ Synthesis and Redox Behavior of Cyanovinyl-Substituted 2H-Cyclohepta[b]furan-2-ones

Taku Shoji,* Junya Higashi, Shunji Ito, Mitsunori Oda, Masafumi Yasunami, and Noboru Morita

*Department of Chemistry, Faculty of Science, Shinshu University, Asahi, Matsumoto 390-8621, Japan

Abstract

Cyanovinyl-substituted 2H-cyclohepta[b]furan-2-ones 3, 4, 5 and 7 were prepared by the Wittig, Knoevenagel and electrophilic substitution reaction, respectively. The intramolecular charge-transfer (ICT) interactions between the 2H-cyclohepta[b]furan-2-one ring and cyanovinyl acceptor moiety were investigated by UV/Vis spectroscopy and theoretical calculations. The redox behavior of these novel compounds was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Significant color changes in these compounds were observed under electrochemical reduction conditions by visible spectroscopy.

■ Selenium Oxide Oxidation of Hexahydro-1,5-imino-3-benzazocine-7,10-dione in Aliphatic Alcohol for Conversion of Renieramycin Marine Natural Products

Mayuko Mori, Naomi Daikuhara, Junya Yamada, and Naoki Saito*

*Meiji College of Pharmacy, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan

Abstract

A selenium oxide oxidation of hexahydro-1,5-imino-3-benzazocine-7,10-dione derivatives in several aliphatic alcohols to generate C-6 ether derivatives stereoselectively is described. This procedure shows promise for the construction of several renieramycins, such as renieramycins B, D, and V. The results of cytotoxicity studies are also presented.

■ Reaction of Grignard Reagents with Diisopropylaminoborane. Synthesis of Alkyl, Aryl, Heteroaryl and Allyl Boronic Acids from Organoc(diisopropyl)aminoborane by a Simple Hydrolysis

Christopher L. Bailey, Chris L. Murphy, Jacob W. Clary, Scott Eagon, Naomi Gould, and Bakthan Singaram*

*Department of Chemistry, University of California, 1156 High Street, Santa Cruz, CA 95064, U.S.A.

Abstract

Diisopropylaminoborane (BH2-N(iPr)2) is prepared by reacting lithium diisopropylaminoborohydride (iPr-LAB) with trimethylsilyl chloride (TMSCl). Aliphatic, aromatic, and heteroaromatic (diisopropylamino)boranes are readily synthesized at ambient temperature (0 °C) in 1h by the reaction of Grignard reagents with (BH2-N(iPr)2). Two contending reaction pathways have tentatively been identified. During the mechanistic investigation, bromomagnesium diisopropylaminoborohydride was identified as a byproduct. This borylation reaction can be carried out under Barbier conditions, where (BH2-N(iPr)2) traps the in situ formed Grignard reagent from the corresponding organic halide and magnesium metal. Simple acid hydrolysis of the product organo(diisopropylamino)borane leads to the corresponding boronic acid in good to excellent yield.

■ Reactions of Amines and Hydrazides derived from L-Proline with Dialkyl Dicyanofumarates

Grzegorz Mlostoń,* Adam M. Pieczonka, Aneta Wróblewska, Anthony Linden, and Heinz Heimgartner*

*Institute of Organic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

Abstract

The reaction of prolinamine derivatives (8a,b) and dialkyl dicyanofumarates (1) in dichloromethane at room temperature leads to the optically active enamines of type (10). Whereas products (10) in the case of 1-benzyl prolinamine (8a) are stable compounds, the corresponding enamines obtained from the non-protected prolinamine (8b) smoothly undergo a cyclocondensation at room temperature to give perhydropyrrolo[1,2-a]pyrazine derivatives (11). The molecular structure of 11a was established by X-Ray crystallography. In analogy to 8a, 1-benzyl prolinehydrazide (9a) and 1b in dichloromethane react to yield the enehydrazine (12b). On the other hand, the reaction of 9a and dicyanofumarates (1) in methanol at room temperature leads to the corresponding dialkyl 3-amino-1H-pyrazole-4,5-dicarboxylates (13) and methyl 1-benzylprolinate (14b) via a stepwise mechanism. The analogous reaction was observed between a 3-oxidoimidazole-4-carbohydrazide (15) and 1b.

■ TRANSITION METALS IN ORGANIC SYNTHESIS, PART 104. IRON-MEDIATED TOTAL SYNTHESIS OF FUROCLAUSINE-A

Micha P. Krahl, Arndt W. Schmidt, and Hans-Joachim Knölker*

*Institute of Organic Chemistry, Technical University Dresden, Bergstrasse 66, D-01069 Dresden, Germany

Abstract

Using iron-mediated coupling reactions a convergent seven-step synthesis of the furo[3,2-a]carbazole alkaloid furoclausine-A is achieved.