HETEROCYCLES

■ Contents

■ Mini-Review: Organic Catalysts in the 1,3-Dipolar Cycloaddition Reactions of Nitrile Oxides

Silvia Roscales* and Joaquín Plumet*

*Complutense University, Faculty of Chemistry, Organic Chemistry Department, Ciudad Universitaria, 28040, Madrid, Spain

Abstract

In 1961, Huisgen categorized the nitrile oxides (NOs) as a member of a broader class of 1,3-dipoles that were capable of undergoing 1,3-dipolar cycloaddition (DC) reactions. Nevertheless, the cycloaddition (CA) reactions of NOs to alkenes and alkynes are in many cases hampered by the tendency to the dimerization of the NO to the related furoxan (1,2,5-oxadiazole 2-oxide). In addition, although monosubstituted alkenes and alkynes show high regioselectivity in their cycloadditions with NOs, 1,2-disubstituted derivatives often give mixtures of regioisomers. Catalyzed NOs cycloadditions constitute in many cases an appropriate response to these problems and, in particular, the metal catalyzed cycloaddition reactions have been extensively used. However, the cost, toxicity and removal of trace amounts of the metal residues from desired products is quite costly and challenging, while crucial, especially in the pharmaceutical industry. Obviously, alternative pathways under metal-free conditions to fulfill the metal-catalyzed reactions are highly appealing. The present review is devoted to the consideration of the use of organic molecules as catalysts for 1,3-dipolar cycloaddition reactions of nitrile oxides.

■ Xanthates and Vinyl Esters, a Remarkably Powerful Alliance

Béatrice Quiclet-Sire and Samir Z. Zard*

*Department of Chemistry, Ecole Polytechnique, CNRS UMR 7652, 91128 Palaiseau, France

Abstract

The present brief overview highlights and discusses the synthetic potential of the degenerative radical addition of xanthates to vinyl esters. The process results in the formation of masked aldehydes bearing numerous functionalities. It allows expedient and convergent syntheses of various structures, including cyclic and open-chain enones, trifluoromethyl enones, dienes, pyrroles, dithietanones, thiophenes, hydroxytetralones, naphthalenes and naphthols.

■ Introducing a Methyl Group into Pyridines and Quinolines: A Mini-Review

Eliezer Falb and Alfred Hassner*

*Department of Chemistry, Bar-Ilan University, Ramat-Gan 5290002, Israel

Abstract

Pyridines are ubiquitous N-heterocycles that are present in many natural products and synthetic drugs with important biological applications. Introduction into a pyridine of a methyl (Me) or an isotopically labeled methyl group at carbon can alter its biological properties. However, regioselective introduction of a Me group in high yield, and preferably in a green manner, is often quite challenging. In this mini-review, several methods, most of which are recent, are examined whereby a Me or CD3 is introduced at a specific carbon in pyridines, as well as in some quinolines.

■ Synthesis of a Tetracyclic Aminobenzimidazole Derivative via Tandem Cyclization of Triphenylguanidine

Yuki Akamatsu, Shinichiro Kamino, and Daisuke Sawada*

*Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 1-1-1, Tsushima-Naka, Kitai-ku, Okayama, 700-8530, Japan

Abstract

We developed a new reaction for the one-pot synthesis of a fused cyclic compound from triphenylguanidine, which was thought to be tandem cyclization, with a moderate yield. In this reaction, conditions such as the metal reagent, oxidant, solvent, and ligand affected whether single or tandem cyclization was preferred.

■ Syntheses and Acid-Stimulus Responsiveness of Aminobenzopyranoxanthene Spiroethers

Ryosuke Hosoda, Shinichiro Kamino,* Masashi Ueda, and Daisuke Sawada*

*Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama-shi, Okayama 700-8530, Japan

Abstract

Novel aminobenzopyranoxanthene spiroethers (ABPX-SEs) based on the spirocyclization of the hydroxymethyl group were synthesized from ABPX spirolactones (ABPX-SLs). The addition of an acid induces a ring-opening reaction to yield two colored monocationic and dicationic spiro-ring species of ABPX. The acid-stimulus responsiveness of the ABPX-SEs is lower than that of ABPX-SLs in polar organic solvents. In addition, the ABPX-SEs exhibit stepwise structural changes of the three equilibrium species at acidic pH, although rapid conversion from the spirolactone to dicationic species occurs in the case of ABPX-SLs.

■ Separation of Minor Actinides from Lanthanides Using Immobilized Ligand Systems: The Role of the Counterion

Ashfaq Afsar, Petr Distler, Laurence M. Harwood,* Jan John, Jasraj S. Babra, Zoe Y. Selfe, Joeseph Cowell, and James Westwood

*Chemical Sciences Division, University of Reading, Whiteknights, Reading RG6 6AD, U.K.

Abstract

A CyMe4-BTPhen functionalized silica gel that selectively extracts Am(III) over Eu(III) from 4 M HNO3 with a separation factor > 154 has been developed. Evidence is presented that the counterion surrounding the M(III) in the proposed 1:1 [BTPhen:M(III)] complex plays an important role in the complexation of Am(III) and Eu(III).

■ α-Glucoside Formation from 2-Deoxy-2-(2,2,2-trichloroethoxycarboxamido)-α-D-glucopyranosyl Acetate Using an Activating System That Used a Combination of Ytterbium(III) Triflate and a Catalytic Boron Trifluoride Diethyl Etherate Complex

Takashi Yamanoi,* Yoshiki Oda, Akihiko Koizumi, Tsubasa Kawaguchi, Shin Yagihara, and Akihiro Yoshida

*Faculty of Pharmacy and Pharmaceutical Sciences, Josai University, 1-1 Keyakidai, Sakado, Saitama 350-0295, Japan

Abstract

This study describes the formation of α-glucoside from 3,4,6-tri-O-benzyl-2-deoxy-2-(2,2,2-trichloroethoxycarboxamido)-α-D-glucopyranosyl acetate using an activating system that used a combination of ytterbium(III) triflate and a catalytic boron trifluoride diethyl etherate complex. This glucoside formation using various types of alcohol acceptors proceeded with high α-stereoselectivity. The novel glucoside method employed in this study is a useful technique for producing 2-amino-2-deoxy-α-D-glucopyranoside derivatives because a 2,2,2-trichloroethoxycarbonyl group from an N-protecting group is easily removable.

■ Tripeptide-Catalyzed Asymmetric Aldol Reaction of Trifluoromethylated Aromatic Ketones with Acetone

Kazumasa Kon, Yoshihito Kohari,* and Miki Murata

*School of Earth, Energy and Environmental Engineering, Faculty of Engineering, Kitami Institute of Technology, 165 Koen-Cho, Kitami, Hokkaido 090-8507, Japan

Abstract

The development of H-Pro-Gly-Ala-OH (3d) to realize an inexpensive and simple organocatalytic system for the direct asymmetric aldol reaction of trifluoromethylated aromatic ketone 1 with acetone was achieved. The 3d-catalyzed aldol reaction of 1a–1j provided various aldol adducts 4a–4j with up to 81% yield and 77% ee. An investigation of the transition state via DFT calculations revealed that hydrogen bonding was important for the revelation of the enantioselectivity.

■ An Intermolecular [4+3] Cycloaddition Reaction Using 3-Hydroxy-2-pyrone Derivatives with an Oxyallyl Cation

Takahiro Suzuki,* Takamune Yanagisawa, and Keiji Tanino*

*Department of Chemistry, Faculty of Science, Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan

Abstract

An intermolecular [4+3] cycloaddition reaction using 3-hydroxy-2-pyrone derivatives with (2-silyloxy)allyl acetate was developed under Brønsted acid conditions to yield highly functionalized seven-membered carbocycles. The transformations of the cycloadducts are described.

■ Synthesis and Stereochemical Analysis of Dynamic Planar Chiral Nine-Membered Diallylic Amide: Significant Substituent Effect on Stereochemical Stability

Jun-ichi Hayashi, Kazuhiro Uehara, Yusuke Ano, Yuuya Kawasaki, Kazunobu Igawa, and Katsuhiko Tomooka*

*Department of Molecular and Material Sciences, Institute for Materials Chemistry and Engineering, and IRCCS, Kyushu University, Kasuga, Fukuoka 816-8580, Japan

Abstract

C4-Methyl substituted nine-membered diallylic cyclic amide 1ac was synthesized. HPLC analysis using a chiral stationary phase revealed the presence of isolable enantiomers, whose absolute stereochemistry were determined by X-ray analysis. Studies on the stereochemical stability of 1ac showed that its chirality is more labile than that of the non-substituted congener 1aa and C3-methyl substituted congener 1ab.

■ Vicinal Functionalization of Uracil Heterocycles with Base Activation of Iodonium(III) Salts

Naoko Takenaga,* Shohei Ueda, Takumi Hayashi, Toshifumi Dohi, and Shinji Kitagaki

*Faculty of Pharmacy, Meijo University, 150 Yagotoyama, Tempaku-ku, Nagoya 468-8503, Japan

Abstract

We describe a new approach for the construction of bicyclic uracil systems and vicinal functionalization by utilizing uracil-iodonium(III) salts. Our method efficiently furnishes various multi-functionalized uracil derivatives in a single step.

■ Synthetic Studies on Pyrroloindolizidine Skeleton Based on Gold–Catalyzed Hydroamination–Enamine Cyclization–Ring–Closing Metathesis Strategy

Kenji Sugimoto,* Natsumi Matsuo, Daisuke Tominaga, and Yuji Matsuya*

*Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan

Abstract

A pyrroloindolizidine skeleton, which is observed in myrmicarin alkaloids isolated from African ant, is highly unique, oligocyclic indolizidine derivative. We describe here an attempt on a synthesis of a pyrroloindolizidine skeleton with our originally developed gold–catalyzed cascade reaction and a newly developed synthetic route for the skeleton via gold–catalyzed hydroamination–enamine cyclization–ring–closing metathesis.

■ Synthesis of LSD1 Inhibitor-Pyrrole-Imidazole Polyamide Conjugates for Region-Specific Alterations of Histone Modification

Rui Qin, Shihori Takayanagi, Yusuke Kondo, Jiawei Li, Naoki Shiga, Masaya Nakajima, Ken-ichi Shinohara, Natsumi Yoda, Takayoshi Suzuki, Atsushi Kaneda, and Tetsuhiro Nemoto*

*Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1, Inohana, Chuo-ku, Chiba 260-8675, Japan

Abstract

Synthetic method of LSD1 inhibitor–pyrrole-imidazole polyamide conjugates for region specific alterations of histone modification is described. A (1S,2R)-tranylcypromine (PCPA) unit was coupled with an L-lysine part using a nosyl strategy. Conjugation of the inhibitor part with PIP tetramer units was achieved by amide bond formation using PyBOP as a condensation reagent.

■ Mechanistic Insight into Catalytic Aerobic Chemoselective α-Oxidation of Acylpyrazoles

Seiya Taninokuchi, Ryo Yazaki,* and Takashi Ohshima*

*Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan

Abstract

Mechanistic studies on catalytic aerobic chemoselective α-oxidation of acylpyrazoles, including control experiments, kinetic isotope effect experiments, and radical clock experiments, are described. The key to promoting the reaction was the in-situ generation of a copper(II) peroxo complex, which serves as a Lewis acid/Brønsted base cooperative catalyst for efficient enolization. The present catalysis was applicable to late-stage α-oxidation of functionalized acylpyrazoles. A preliminary diastereoselective reaction using readily available chiral acylpyrazoles demonstrated that the present catalysis provided access to optically active α-hydroxy acid derivatives.

■ Rapid Stereoselective Syntheses of Heteroarene-Fused Azacycles via Diastereoselective Conjugate Addition of Heteroaryl Substituted Lithium Amides

Stephen G. Davies,* Ai M. Fletcher, Katherine E. Holder, Paul M. Roberts, James E. Thomson, and David Zimmer

*Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, U.K.

Abstract

Conjugate addition of heteroaryl substituted lithium amides to a range of α,β-unsaturated esters followed by in situ enolate oxidation with (–)-(camphorsulfonyl)oxaziridine gave the corresponding α-hydroxy-β-amino esters. Subsequent Friedel-Crafts type cyclisation of these α-hydroxy-β-amino esters gave a range of heteroarene-fused azacycles in good yields and high diastereoselectivities.

■ Synthesis, Conformation, and Biological Activities of a Des-A-Ring Analog of 18-Deoxy-Aplog-1, a Simplified Analog of Debromoaplysiatoxin

Yoshiki Ashida, Ryo C. Yanagita,* Yasuhiro Kawanami, Mutsumi Okamura, Shingo Dan, and Kazuhiro Irie

*Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, 2393 Ikenobe, Miki, Kagawa 761-0795, Japan

Abstract

10-Me-Aplog-1 as a simplified analog of tumor-promoting debromoaplysiatoxin and a potent activator of protein kinase C (PKC) is a promising chemotherapeutic agent. In this study, we synthesized a des-A-ring analog (4) of 18-deoxy-aplog-1 as a synthetically-accessible analog. Compound 4 retained the conformation of the PKC-recognition part of aplogs. Moderate affinity for conventional PKC isozymes (α, β, γ) and anti-proliferative activity against NCI-H460 (lung) and MKN45 (stomach) human cancer cell lines were observed. The results suggest that 4 could serve as a lead compound for the development of conventional PKC isozyme-selective chemotherapeutic agents.

■ Mn(III)-Based Oxidative Radical Ring-Expansion Reaction Using Squarate Derivatives: Selective Synthesis of Bis(butenolide)s and the Acetate Monomers

Jun-ichi Sasaki, Makoto Kobayashi, Yûsuke Ibe, and Hiroshi Nishino*

*Department of Chemistry, Graduate School of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan

Abstract

The Mn(III)-based oxidation of phenyl- and alkyl-substituted hydroxycyclobutenones selectively produced the bis(butenolide)s or the acetate monomers via the 5-endo radical cyclization depending upon the concentration of the reaction. A similar reaction of hydroxycyclobutenones bearing an alkenyl and alkynyl substituent did not produce any bis(butenolide)s or acetate monomers, but the 5-exo and 6-endo radical cyclization products including the unsaturated group. The oxidation of the hydroxycyclobutenones having an unsaturated substituent in the presence of alkenes afforded radical coupling products during the 5-exo radical cyclization. The reaction details, structure determination of the products, and the mechanism for the formation of the products are described.

■ Enantioselective Synthesis of 2,4,5-Trisubstituted Tetrahydropyrans via Peptide-Catalyzed Michael Addition Followed by Kishi’s Reductive Cyclization

Atsushi Ueda,* Mei Higuchi, Tomohiro Umeno, and Masakazu Tanaka*

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

Abstract

An enantioselective synthesis of 2,4,5-trisubstituted tetrahydropyrans has been achieved in four steps from α,β-unsaturated ketones and dimethyl malonate by peptide-catalyzed asymmetric Michael addition and diastereoselective construction of tetrahydropyran rings by Kishi’s reductive cyclization as key steps. A variety of α,β-unsaturated ketones were converted to the 1,4-products with high enantioselectivities (83–98% ee).

■ The Practical Synthesis of Dissymmetrical 1,3,5-Trioxazatriquinane Derivatives Comprised of Three Distinct Carbonyl Compounds

Shigeto Hirayama, Koji Obayashi, Naohisa Wada, Kousuke Ohyama, Shizuho Fuku, Koji Koyano, Fumika Karaki, Kennosuke Itoh, Hiroshi Nagase, and Hideaki Fujii*

*Laboratory of Medicinal Chemistry, School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan

Abstract

We have previously synthesized various 1,3,5-trioxazatriquinane derivatives consisting of not only three identical carbonyl compounds but also two identical carbonyl moieties as well as another type of carbonyl compound. However, dissymmetrical derivatives prepared from three distinct carbonyl compounds have not yet been selectively synthesized. Herein, we developed a selective synthetic method of such dissymmetrical derivatives: free　α-hydroxyaldehydes were slowly added to a solution of protected　α-hydroxyaldehydes, ammonium chloride, and sodium acetate to selectively provide key intermediate oxazolines, which were successfully converted into the objective dissymmetrical derivatives.

■ β-Trichloroacetylation of Cyclic Amines: Application to Synthesis of Chiral Azabicyclo-N-oxyls

Masami Kuriyama, Satoshi Kamogawa, Kosuke Yamamoto, and Osamu Onomura*

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

Abstract

β-Trichloroacetylation of cyclic amines was developed under mild reaction conditions, and the desired trichloroacetylated products were obtained in good yields. This method was applied to the preparation of optically active azabicyclo compounds, which were converted to chiral azabicyclo-N-oxyls.

■ Synthesis and Evaluation of Topoisomerase I Inhibitors Possessing the 5,13-Dihydro-6H-benzo[6,7]indolo[3,2-c]quinolin-6-one Scaffold

Tsutomu Fukuda,* Yuri Matsuo, Fuyuki Matsuoka, Naoki Yoshioka, Gen Onodera, Masanari Kimura, Fumito Ishibashi, and Masatomo Iwao

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

Abstract

Novel topoisomerase I inhibitors possessing the 5,13-dihydro- 6H-benzo[6,7]indolo[3,2-c]quinolin-6-one (BIQ) scaffold were designed and synthesized. This scaffold was constructed using sequential and regioselective functionalization of the pyrrole core through palladium-catalyzed cross-coupling, conventional electrophilic substitution, directed lithiation, and subsequent diphenylphosphoryl azide (DPPA)-mediated lactam ring construction. The obtained BIQs were evaluated for their topoisomerase I inhibitory activities and their antiproliferative activities in the panel of 39 human cancer cell lines established by the Japanese Foundation for Cancer Research (JFCR39).

■ Synthesis of Diverse 3-Azido-5-(azidomethyl)benzene Derivatives via Formal C–H Azidation and Functional Group-Selective Transformations

Yoshitake Nishiyama, Yoshihiro Misawa, Yuki Hazama, Kazuhiro Oya, Suguru Yoshida,* and Takamitsu Hosoya*

*Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan

Abstract

3-Azido-5-(azidomethyl)benzene derivatives are useful compounds for preparing diverse bistriazole compounds and photoaffinity probes for target identification of bioactive compounds. To more easily synthesize a diverse range of diazido compounds, a facile method for synthesizing diazido compounds bearing a transformable functional group, such as iodo, bromo, methoxycarbonyl, or cyano group, was developed. This method is based on formal C–H azidation of 1,3-disubstituted benzenes via regioselective borylation followed by deborylative azidation, with subsequent transformations, such as that of a one-carbon unit on the benzene ring to an azidomethyl group. The functional groups of the diazido compounds were efficiently transformed to various connecting groups, including carboxy, (succinimidyloxy)carbonyl, hydroxymethyl, formyl, bromomethyl, tosylthiomethyl, ethynyl, diazoacetyl, bromoacetyl, boryl, hydroxy, aminocarbonyl, amino, and isothiocyanato groups, leaving the azido groups untouched. Several diazido building blocks were used to prepare diazido compounds by forming amide, thiourea, and sulfide bonds via conjugation at the connecting groups. These results show that the method described here would facilitate diazido probe syntheses and bistriazole library construction.

■ Asymmetric Synthesis of 2,3-Dimethoxy-8-oxoberbine, Precursor of O-Methylbharatamine

Maria Chrzanowska,* Agnieszka Dreas, and Zofia Meissner

*Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznań, Poland

Abstract

The enantiospecific and enantioselective syntheses of 2,3-dimethoxy-8-oxoberbine were performed using the lateral metallation methodology. In the enantiospecific synthesis (4S)-2,2,4-trimethyl-3-(o-toluoyl)oxazolidine incorporating (S)-alaninol as the chiral auxiliary was applied. The addition reaction of benzylic anion generated in situ from chiral oxazolidine into 6,7-dimethoxy-3,4-dihydroisoquinoline led to the protoberberine with high enantiomeric excess. Enantioselective synthesis of 2,3-dimethoxy-8-oxoberbine was performed with achiral 2,2-dimethyl-3-(o-toluoyl)oxazolidine in the presence of chiral ligands. Among them (–)-sparteine and (+)-sparteine surrogate turned out to be the most efficient ones.

■ Second-Generation Synthesis of a Chiral Building Block for Oxygenated Terpenoids via a Ring-Contractive Coupling with a Secondary Alcohol

Sayuri Saito, Hiroyuki Yamakoshi, and Seiichi Nakamura*

*Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan

Abstract

A much improved second-generation synthesis of a chiral building block, developed for the syntheses of C17-oxygenated steroids/triterpenoids and C9-oxygenated labdane diterpenoids, was accomplished by exploiting a ring-contractive coupling between an α-bromo-δ-valerolactone and (R)-seudenol, wherein the use of t-BuOK as a base allowed clean conversion to the corresponding tetrahydrofuran-2-carboxylate even with a small excess of the alcohol component.

■ Consice Synthesis of TAN1251C

Yosuke Nagasaka, Tomohiro Asakawa, Sayaka Shintaku, Akitaka Masuda, Kosuke Matsumura, Makoto Inai, Yoshinobu Ishikawa, Masahiro Egi, Yoshitaka Hamashima, and Toshiyuki Kan*

*School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka-shi, 422-8526, Japan

Abstract

An efficient total synthesis of TAN1251C was accomplished by employing Ugi four-component condensation reaction and Dieckmann condensation to construct the spiro-fused cyclohexanone and γ-lactam ring structure. Diastereoselective reduction by side-chain-controlled hydrogenation of enamide 37 or Zn reduction of oxime 48 enabled construction of the amino group with the desired stereochemistry.

■ The Effect of Lithium Ion on the Stereoselectivity of the Intramolecular Michael Addition of an N-Arylsulfoximine Anion

Aswin Garimalla, Quin Long, Christopher J. Cramer,* and Michael Harmata*

*Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211, USA.

Abstract

The stereochemical outcome of the intramolecular Michael addition of a sulfoximine carbanion to a Z-configured α,β-unsaturated ester is dependent on lithium ion coordination between the oxygen on the sulfoximine and the carbonyl oxygen of the ester, based on both experimental and computational studies. Formally, this leads to a more sterically congested structure than might otherwise be preferred. Indeed, addition of HMPA, a substance capable of effective solvation of lithium cations, changes the stereochemical course of the reaction dramatically.

■ Synthesis of N-Heterocyclic Carbene Ligands for Site-Selective C-H Alkylation by Cooperative Nickel/Aluminum Catalysis

Shogo Okumura, Tomohiro Ebara, Kazuhiko Semba, and Yoshiaki Nakao*

*Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoudai-katsura, Nishikyo, Kyoto 615-8510, Japan

Abstract

We report synthesis of N-heterocyclic carbenes (NHCs), N,N'-bis{2,6-bis(3,5-dialkylphenyl)methy-4-methoxyphenyl}imidazol-2-ylidenes {alkyl = ethyl (L2) or n-propyl (L3)} and their applications to nickel-catalyzed C–H alkylation reactions of arenes. They showed site-selectivities and/or yields higher than NHCs used previously for the reactions.

■ Synthesis and Properties of a Tricyclic Hexaketone Monohydrate with Hexabutyl Side Chain

Mio Ishita, Masanori Ohkoshi, Yoshiyuki Kuwatani, Hiroyuki Otani, Tohru Nishinaga, and Masahiko Iyoda*

*Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan

Abstract

A tricyclic hexaketone monohydrate with a hemiacetal structure was synthesized by the ruthenium-catalyzed oxidation of butyl-substituted tribenzotetradehydro[12]annulene-1,2-dione. The oxidation of the annulenedione afforded unique [12]annulene-1,2,5,6,9,10-hexaone, followed by the cyclization to produce corresponding tricyclic hydrate containing two dihydrobenzopyranone rings. The tricyclic hexaketone hydrate weakly interacts with methanol and ethylene glycol to form 1:1 complexes in solution.

■ Packing and Thin-Film Structures of 5,7,12,14-Tetra(α-alkylthienylethyl)pentacenes

Hiroki Makino, Shin Sato, Junro Yoshino, Naoto Hayashi,* and Hiroyuki Okada*

*Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan

Abstract

Four 5,7,12,14-tetra(thienylethynyl)pentacenes (2–5) bearing H, Me, C5H11, and C6H13 groups at the α-positions of the thienyl groups were synthesized. The α-alkylthienyl groups enhanced solubilities of 2–5, whereas their ultraviolet/visible spectra were virtually identical. X-Ray diffraction revealed that the packing structure of 4 and 5 were significantly different because of one methylene group in each alkyl group. The thin-film structure of 4 was amorphous, while that of 5 consisted of small crystalline needles. Neither 4 nor 5 behaved as organic field-effect transistors because of inadequate packing and thin-film structure.