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ABSTRACT: A benzyne-mediated synthesis of substituted indolines and carbazoles was developed. The reaction includes generation of benzyne using Mg(TMP)2·2LiCl as a base, cyclization, and trapping the resulting organomagnesium intermediate with an electrophile to provide a series of substituted indolines and carbazoles in a regiospecific manner. This was applied to a concise five-pot total synthesis of heptaphylline.
Organic Letters 04/2013; · 5.86 Impact Factor
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ABSTRACT: The key step in this total synthesis of (-)-acetylaranotin is the efficient formation of the characteristic dihydrooxepine ring from cyclohexenone through an unusual vinylogous Rubottom oxidation and a regioselective Baeyer-Villiger oxidation. (-)-Acetylaranotin is obtained in 22 steps from commercially available L-Cbz-tyrosine (Cbz=benzyloxycarbonyl).
Angewandte Chemie International Edition 11/2012; · 13.45 Impact Factor
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ABSTRACT: An efficient approach to generate a fully functionalized cyclopenta[a]phenanthrene 34, the basic carbon framework of andrastin C (1c), is described. The present synthetic route features a stereoselective intramolecular Diels-Alder reaction of triene 12 and an intramolecular carbonyl ene reaction of 3-phenanthrenyl-2-(methoxymethoxy)propanal 31.
The Journal of Organic Chemistry 10/2012; · 4.45 Impact Factor
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ABSTRACT: A concise total synthesis of (-)-mersicarpine from a known cyclohexanone was accomplished. The azepinoindole core was constructed by a DIBAL-H-mediated reductive ring-expansion reaction of oxime.
Organic Letters 04/2012; 14(9):2320-2. · 5.86 Impact Factor
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ABSTRACT: The ring-expansion reactions of heterocyclic ketoximes and carbocyclic ketoximes with several reductants such as AlHCl2, AlH3 (alane), LiAlH4, LiAlH(OtBu)3, and (MeOCH2CH2O)2AlH2Na (Red-Al) were examined. Among reductants, AlHCl2 (LiAlH4:AlCl3 = 1:3) in cyclopentyl methyl ether (CPME) has been found to be a suitable reagent for the reaction, and the rearranged cyclic secondary amines were obtained in good to excellent yields.
Molecules 01/2012; 17(6):7348-55. · 2.39 Impact Factor
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ABSTRACT: A triflic imide (Tf(2)NH) catalyzed isomerization of kinetically favourable silyl enol ethers into thermodynamically stable ones was developed. We also demonstrated a one-pot catalytic reaction consisting of (2 + 2) cycloaddition and isomerization. In the reaction sequence, Tf(2)NH catalyzes both of the reactions.
Beilstein Journal of Organic Chemistry 01/2012; 8:658-61. · 2.52 Impact Factor
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Angewandte Chemie International Edition 05/2011; 50(21):4884-7. · 13.45 Impact Factor
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ABSTRACT: A highly efficient total synthesis of dictyodendrins A-E was accomplished. The synthesis features a novel benzyne-mediated one-pot indoline formation/cross-coupling sequence for the construction of a highly substituted key indoline intermediate. Peripheral substituents were introduced onto this intermediate in a modular fashion to complete the total synthesis of dictyodendrins A-E.
Chemistry - An Asian Journal 10/2010; 6(2):560-72. · 4.50 Impact Factor
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ABSTRACT: The enantioselective total synthesis of (-)- and (+)-petrosin is described. The union of two key segments was executed by Suzuki-Miyaura coupling. The quinolizidine rings were stereoselectively constructed via a diastereoselective Mannich reaction and an aza-Michael reaction. The 16-membered ring was constructed by ring-closing metathesis with the second-generation Grubbs catalyst.
Organic Letters 10/2010; 12(22):5196-9. · 5.86 Impact Factor
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Angewandte Chemie International Edition 08/2010; 49(34):5925-9. · 13.45 Impact Factor
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ABSTRACT: A concise total synthesis of PDE-II featuring copper-mediated double aryl amination with the combination of CuI, CsOAc, and Cs2CO3 is described. The highly substituted pyrroloindole skeleton was constructed by a one-pot five-step sequence including double aryl amination, beta-elimination, deprotection of a Cbz group, and removal of an Ns group followed by rearomatization.
Chemical Communications 04/2010; 46(15):2641-3. · 6.17 Impact Factor
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ABSTRACT: Vinblastine has been widely known as a prominent agent in cancer chemotherapy, and in order to search for more potent drugs, various analogs have been derived from natural products. However, because modifications of natural products have limited classes of derivatives, an efficient synthetic route toward vinblastine has been required.Herein a stereocontrolled total synthesis of (+)-vinblastine is described. The synthesis of the upper half features a stereoselective construction of the tertiary alcohol through a 1,3-dipolar cycloaddition of nitrile oxide and a Baeyer-Villiger oxidation, a facile indole formation utilizing a radical cyclization of o-alkenylthioanilide, and a macrocyclization of 2-nitrobenzenesulfonamide. The crucial coupling of the upper half with synthetic vindoline was successfully performed to furnish the coupling product in nearly quantitative yield, and subsequent transformations provided (+)-vinblastine.
The Chemical Record 04/2010; 10(2):101-18. · 4.38 Impact Factor
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ABSTRACT: A systematic investigation of the reductive ring-expansion reaction of cyclic ketoximes fused to aromatic rings with diisobutylaluminum hydride (DIBALH) is described. This reaction regioselectively afforded a variety of five- to eight-membered bicyclic heterocycles or tricyclic heterocycles containing nitrogen neighboring an aromatic ring, including indoline, 1,2,3,4,5,6-hexahydrobenz[b]azocine, 3,4-dihydro-2H-benzo[b][1,4]oxazine, 2,3,4,5-tetrahydrobenzo[b][1,4]thiazepine, 1,2,3,4,5,6-hexahydroazepino[3,2-b]indole, 2,3,4,5-tetrahydro-1H-benzothieno[2,3-b]azepine, 2,3,4,5-tetrahydro-1H-benzothieno[3,2-b]azepine, 5,6-dihydrophenanthridine, and 5,6,11,12-tetrahydrodibenz[b, f]azocine. The reaction mechanism leading to the rearrangement was investigated on the basis of the restricted Becke three-parameter plus Lee-Yang-Parr (B3LYP) density functional theory (DFT) with the 6-31G (d) basis set. It was found that the reaction proceeds through a three-centered transition state via a stepwise mechanism because the potential energy curve along the intrinsic reaction coordinate (IRC) had two maxima (saddle points; TS1 and TS2) and the partial phenonium cation intermediate C. In addition to cyclic ketoximes fused to aromatic rings, the reactions of various cyclic and acyclic ketoximes were examined to investigate preference of migrating group. It was found that the more electron-rich group migrated preferentially to give the corresponding secondary amines.
The Journal of Organic Chemistry 02/2010; 75(3):627-36. · 4.45 Impact Factor
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Angewandte Chemie International Edition 10/2009; · 13.45 Impact Factor
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Angewandte Chemie International Edition 09/2009; 48(41):7454. · 13.45 Impact Factor
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ABSTRACT: We demonstrated a catalytic cascade inverse electron demand hetero-Diels-Alder reaction (Povarov reaction) and hydrogen-transfer process. The reaction of electron-rich olefins and excess amount of imines in the presence of acid catalysts under appropriate conditions affords substituted quinolines in a single operation. In the cascade process, the catalysts, such as Tf2NH, TfOH, and Lewis acids, catalyze two mechanistically distinct reactions (auto-tandem catalysis). We also describe the synthetic utility of the prepared quinolines.
The Journal of Organic Chemistry 09/2008; 73(19):7451-6. · 4.45 Impact Factor
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ABSTRACT: We describe here (2+2) cycloaddition reaction of alkyl enol ethers with acrylates catalyzed by triethylsilyl triflic imide (Et3SiNTf2), which was in situ generated from triethylsilane and triflic imide. The reaction efficiently provides substituted cyclobutanes bearing alkoxy function in a stereoselective manner.
CHEMICAL & PHARMACEUTICAL BULLETIN 09/2008; 56(8):1205-6. · 1.59 Impact Factor
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ABSTRACT: An improved synthesis of the indole unit, a key intermediate for eudistomin C, was established utilizing Makosza's indole synthesis. A concise total synthesis of eudistomin E was achieved on the basis of the improved synthesis.
Organic Letters 07/2008; 10(12):2369-72. · 5.86 Impact Factor
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ABSTRACT: A total synthesis of (-)-kainic acid starting from the commercially available 2-azetidinone is described. The key delta-lactone intermediate was concisely prepared from the commercially available azetidinone through the Reformatsky-type reaction and an introduction of a glycine moiety. The construction of the functionalized pyrrolidine ring was executed by a one-pot sequential elimination-Michael addition protocol of a beta-amino-delta-lactone intermediate with high diastereoselectivity.
Organic Letters 06/2008; 10(9):1711-4. · 5.86 Impact Factor
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ABSTRACT: A convergent total synthesis of (+)-yatakemycin was accomplished by a 20-step sequence in 13% overall yield. The regioselective ring opening of (S)-epichlorohydrin with a 2,6-dibromophenyllithium derivative enabled us to introduce a chiral carbon center, which was required for the stereoselective construction of the cyclopropane ring. The five aryl-nitrogen bonds in (+)-yatakemycin were constructed by a mild copper-mediated aryl amination that utilized the combination of CuI with CsOAc. The efficient and chemoselective debenzylation of aryl benzyl ether with BCl3 in the presence of pentamethylbenzene was developed. With these new methodologies, the subgram-scale synthesis of (+)-yatakemycin was achieved.
Chemistry - An Asian Journal 03/2008; 3(2):296-309. · 4.50 Impact Factor
