Thiourea-catalyzed Diels–Alder reaction of a naphthoquinone monoketal dienophile

• Carsten S. Kramer and
• Stefan Bräse

Beilstein J. Org. Chem. 2013, 9, 1414–1418, doi:10.3762/bjoc.9.158

• -Leopoldshafen, Germany 10.3762/bjoc.9.158 Abstract A variety of organocatalysts were screened for the catalysis of the naphthoquinone monoketal Diels–Alder reaction. In this study we found that Schreiner's thiourea catalyst 10 and Jacobson's thiourea catalyst 12 facilitate the cycloaddition of the sterically

• hindered naphthoquinone monoketal dienophile 3 with diene 4. The use of thiourea catalysis allowed for the first time the highly selective synthesis of the exo-product 2a in up to 63% yield. In this reaction a new quaternary center was built. The so formed cycloaddition product 2a represents the ABC

• ][8]. In our recent studies towards a synthetic access to the natural product beticolin 0 (1) [9] (Scheme 1), we have found that naphthoquinone monoketals are suitable building blocks for our designed synthesis [9]. In our retrosynthetic approach, the naphthoquinone monoketal dienophile 3 was found to

Synthesis of 2,3-dihydronaphtho[2,3-d][1,3]thiazole-4,9-diones and 2,3-dihydroanthra[2,3-d][1,3]thiazole-4,11-diones and novel ring contraction and fusion reaction of 3H-spiro[1,3-thiazole-2,1'-cyclohexanes] into 2,3,4,5-tetrahydro-1H-carbazole-6,11-diones

• Lidia S. Konstantinova,
• Kirill A. Lysov,
• Ljudmila I. Souvorova and
• Oleg A. Rakitin

Beilstein J. Org. Chem. 2013, 9, 577–584, doi:10.3762/bjoc.9.62

• -naphthoquinone structure is common for various natural products. It is associated with numerous biological activities, such as enzyme-inhibitory, antifungal, antibacterial, anticancer, antiproliferative, antiplatelet, anti-inflammatory, antiallergic, and antimalarial ones. Benzoquinones fused with heterocycles

• range, and low side effects it seemed quite promising to incorporate two heteroatoms into the heterocycle attached to the naphthoquinone (e.g., thiazole) core. Despite continuous interest in 1,4-naphthoquinones fused with heterocycles, only a limited number of thiazolonaphthoquinones have been known so

• -[butyl(methyl)amino]naphthoquinone 3a with sulfur monochloride and tertiary amines [N-ethyldiisopropylamine (Hünig’s base) and 1,4-diazabicyclooctane (DABCO)]. Treatment of naphthoquinone 3a with S2Cl2 (9 equiv) and Hünig’s base (5 equiv) in THF at 0 °C for 72 h with subsequent heating under reflux for 2

Organocatalytic asymmetric Michael addition of unprotected 3-substituted oxindoles to 1,4-naphthoquinone

• Jin-Sheng Yu,
• Feng Zhou,
• Yun-Lin Liu and
• Jian Zhou

Beilstein J. Org. Chem. 2012, 8, 1360–1365, doi:10.3762/bjoc.8.157

• Michael addition of unprotected 3-prochiral oxindoles 1 to 1,4-naphthoquinone. Quinidine derivative (DHQD)2PYR was found to be able to catalyze this reaction in up to 83% ee, with moderate to excellent yields. This method could be used for the synthesis of enantioenriched 3,3-diaryloxindoles, and the

• to report our initial results about the catalytic asymmetric Michael addition of unprotected 3-prochiral oxindoles to 1,4-naphthoquinone. Results and Discussion We began the reaction development by the evaluation of different chiral catalysts derived from cinchona alkaloids in the reaction of 3

• -phenyloxindole 1a and 1,4-naphthoquinone (2a), with ethyl acetate (EtOAc) as the solvent at 0 °C (Table 1, Figure 1). A variety of bifunctional cinchona alkaloid-derived catalysts 5–9 were first tried, aiming to facilitate the reaction by the dual activation of both reaction partners, with H-bonding donor moiety

Enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinones to nitroalkenes catalyzed by binaphthyl-derived organocatalysts

• Saet Byeol Woo and
• Dae Young Kim

Beilstein J. Org. Chem. 2012, 8, 699–704, doi:10.3762/bjoc.8.78

• ; Introduction Quinone and naphthoquinone structures exist in a large number of natural products and biologically active molecules [1][2][3][4]. Many of these naturally occurring naphthoquinones and their synthetic analogues are important precursors for the synthesis of natural products and pharmaceuticals [5][6

• reported the enantioselective Michael addition of active methines to nitroalkenes [43][44]. Herein, we describe the direct enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinone with nitroalkenes, catalyzed by bifunctional organocatalysts (Figure 1) that bear both central and axial chiral

• elements [45][46][47]. We initially investigated the reaction system with 2-hydroxy-1,4-naphthoquinone (1) and nitrostyrene 2a in the presence of 10 mol % of Takemoto's catalyst I in acetonitrile at room temperature, to determine the optimum reaction conditions for the catalytic, enantioselective Michael

Synthesis of 2a,8b-Dihydrocyclobuta[a]naphthalene-3,4-diones

• Kerstin Schmidt and
• Paul Margaretha

Beilstein J. Org. Chem. 2010, 6, No. 76, doi:10.3762/bjoc.6.76

• % (isolated yield) of mixed photocycloadducts 2. Careful acidic hydrolysis of the acetal function of 2 gives the title compounds 3, the overall sequence representing a first approach to a (formal) [2 + 2] photocycloadduct of a 1,2-naphthoquinone to an alkyne. Keywords: cyclobutenes; photocycloaddition

• -diones, i.e. (formal) 1,2-naphthoquinone + alkyne [2 + 2] cycloadducts. Results Irradiation of 1 in the presence of alkynes affords the – known [3] – pentacyclic dimers and variable amounts (0–33%) of enone + alkyne cycloadducts as indicated by 1H NMR spectroscopy. The yields of mixed cycloadducts with

• relative yield (33%) of compounds 2a or 2b at total conversion of starting material is acceptable. Moreover, the fact that hydrolysis of the cycloadducts proceeds quantitatively, then the overall yields in the preparation of the – novel – 1,2-naphthoquinone + alkyne cycloadducts even becomes satisfactory

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• low twisting ability. The structure of the dopants under investigation was determined by DFT calculations at the B3LYP/6-31g** level [58]; the optimized geometries are shown in Figure 3. In the dihydro[5]helicene quinones and bisquinones 1–5, the naphthoquinone rings are approximately planar, with

Diastereoselective and enantioselective reduction of tetralin- 1,4-dione

• E. Peter Kündig and
• Alvaro Enriquez-Garcia

Beilstein J. Org. Chem. 2008, 4, No. 37, doi:10.3762/bjoc.4.37

• ; Introduction In this article, we briefly review synthetic approaches to 2,3-dihydro-1,4-naphthoquinone, more simply named tetralin-1,4-dione (2). This symmetric diketone is the stable tautomer of 1,4-dihydroxynaphthalene (1). Although known for many years, it has never been used in synthesis. The reactions of

• being the largely dominant species in solution [4]. Tetralin-1,4-dione (2) has also been obtained by catalytic hydrogenation of 1,4-naphthoquinone (3) using Wilkinson’s catalyst (70% yield) [5], by oxidation of 1-tetralone (4) with t-BuOOH and a dirhodium caprolactamate catalyst (27% yield at 29

2-Arylhydrazononitriles as building blocks in heterocyclic synthesis: A novel route to 2-substituted- 1,2,3-triazoles and 1,2,3-triazolo[4,5-b]pyridines

• Saleh M. Al-Mousawi and
• Moustafa Sh. Moustafa

Beilstein J. Org. Chem. 2007, 3, No. 12, doi:10.1186/1860-5397-3-12

• as in 5 and therefore excluding 7 (Scheme 2). Typical of enaminones, compound 9 reacts with naphthoquinone to yield the benzofuran 12 and with hydrazine hydrate to yield pyrazolyl-1,2,3-triazole 13 in good yields. Attempts to convert 4 into oxadiazolylhydrazone 6 by heating in DMF afforded 14 whose

Variations in product in reactions of naphthoquinone with primary amines

• Marjit W. Singh,
• Anirban Karmakar,
• Nilotpal Barooah and
• Jubaraj B. Baruah

Beilstein J. Org. Chem. 2007, 3, No. 10, doi:10.1186/1860-5397-3-10

• Marjit W. Singh Anirban Karmakar Nilotpal Barooah Jubaraj B. Baruah Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039 Assam, India 10.1186/1860-5397-3-10 Abstract Reaction of 1,2-naphthoquinone with primary amines gives a 2-amino-1,4-naphthoquinone derivative

• which is equivalent to 1,2 to 1,4 carbonyl transposition. For example the reaction of 1,2-naphthoquinone with 4-methoxyaniline gives 2-(4-methoxyanilino)-naphthoquinone-1,4-(4-methoxyanil) (1) and with n-butylamine gives 2-(butylamino)-naphthoquinone-1,4-butylimine (2) respectively. The compounds 1 and

• 2 are characterized by X-ray crystallography; they have hydrogen-bonded dimeric structures. Similar reaction of 1,4-naphthoquinone with 3-picolylamine and 4-picolylamine gives the corresponding 2-amino 1,4-naphthoquinones; two products are characterized by X-ray crystallography. The reaction of 1,4