Search

[Display omitted] A simple yet efficient approach towards the synthesis of β -hydroxy selanylated ketones was developed from easily accessible chalcones and diphenyl diselenide through an electrochemical pathway. In this technique, diphenyl diselenide and water are the source of PhSe. and hydroxyl (–OH) groups that can be inserted at the α and β positions respectively producing β -hydroxy selanylated ketones in moderate to good yields. The reaction features difunctionalization of ketones, catalyst free, mild reaction conditions, stereo and regioselectivity in an undivided electrochemical cell at room temperature. For this transformation, a plausible radical mechanism has been put out. [ABSTRACT FROM AUTHOR]

We herein report a serendipitously observed acid mediated rearrangement of monoethylene ketal of 2-methyl-2-(3-methylbut-2-en-1-yl)cyclohex-4-ene-1,3-diones to Dihydrobenzopyran and demonstrated the application of this methodology in the construction of core carbon scaffolds of dimethoxyajacareubin, cariphenone-A and crotamadine. [ABSTRACT FROM AUTHOR]

A facile and efficient base promoted one-pot dimerization of halo cyclohexene derivatives leading to a de novo synthesis of biologically important diarylmethane and diarylmethanone derivatives is reported. A plausible mechanism for the unexpected formation of the title compounds involves dehydrohalogenation, 1,6-conjugate addition, subsequent aromatization through C–C bond cleavage and dehydrohalogenation. [ABSTRACT FROM AUTHOR]

A macrocyclic furanobutenolide was crafted from readily available furan building-blocks to set-up a transannular Diels–Alder reaction which delivered the carbocyclic core present in a class of cembranoid diterpene natural products. [ABSTRACT FROM AUTHOR]

Total syntheses of two antimicrobial natural products (±)-cis-neocnidilide and (±)-trans-neocnidilide starting from a readily preparable cyclohexa[b]-fused 5-oxabicyclo[2.1.1]hexane derivative are presented. The diastereomeric tetrahydrofuran tricarboxylate epimers obtained from a BF3⋅OEt2 promoted Grob-type fragmentation of the oxa-bicycle derivative were converted into title natural products by employing pyridinium dichromate/acetic anhydride mediated bis-oxidative cleavage reaction. [ABSTRACT FROM AUTHOR]

Abstract: A formal synthesis of marine-derived antitumor natural product varitriol from a 5-oxabicyclo[2.1.1]hexane derivative is described. A tetrahydrofuran unit of varitriol embedded with four contiguous stereocenters was synthesized with an overall yield of 10.2% in 11 steps from an oxa-bicyclic system. An unprecedented oxidative cleavage reaction involving scissoring of two C C bonds at oxa-quaternary carbon of THFs leading to γ-butyrolactones was reported and a plausible mechanism has been proposed. [Copyright &y& Elsevier]

Abstract: A total synthesis of bioactive tetracyclic natural product paracaseolide A, embodying an architecturally unusual oxa-bowl framework, has been accomplished from commercially available 5-methyl-2-furfural. The key step involving a thermal [4+2]-dimerization of an appropriately crafted 5-methyl-3-alkenylbutenolide is shown to proceed in a stepwise manner. [Copyright &y& Elsevier]

Abstract: A facile transformation of pentasubstituted tribromophenol derivatives to the corresponding alkyl-substituted dibromo-p-benzoquinones has been achieved using PbO2 as oxidizing agent in combination with 60% aq HClO4 in acetone in 70–72% yields. The electrochemical properties of these quinones were studied by means of cyclic voltammetry and compared with p-benzoquinone (BQ) and 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) recorded under identical experimental conditions. [Copyright &y& Elsevier]

Abstract: Nucleophilic racemic amines have been synthesized utilizing a C7nC5x free-radical cascade reaction from a bis-allyl amine starting material. Being potentially useful organocatalytic bases as is evident from their screening in the Baylis–Hillman reaction, optically pure amines were also synthesized from optically pure aldehydes (−) or (+)-4. Bis-allyl amides under similar radical reaction condition resulted in C7n cyclized products. [Copyright &y& Elsevier]

Abstract: Palladium(II)-catalyzed oxidative cyclization of methyl 2-allyl-4,5,6-tribromo-3-hydroxybenzoate 4 gave a mixture of methyl 5,6,7-tribromo-2-methyl-benzofuran-4-carboxylate 5 and methyl 6,7,8-tribromo-2H-1-benzopyran-5-carboxylate 6; the ratio of the two products varied between 71:29 and 24:76 depending on the reaction conditions. On the other hand, NBS or NIS mediated cyclization of 4 followed by treatment with NaOMe or DBU furnished benzofuran derivative 5 in good overall yield. [Copyright &y& Elsevier]

Abstract: An efficient stereoselective synthesis of both the diastereomers of diquinane-based conformationally constrained symmetric bis-γ-lactones starting from tricyclic derivative 9 is reported. The key step involves the intramolecular ring opening of an epoxide by the in situ formed hydrate of a diketone leading to the tetracyclic hemiacetal 10, which directly leads to the exo-hydroxy bis-γ-lactone derivatives 2 and 4 under basic hydrogen peroxide cleavage conditions. Conversion to the endo-hydroxy bis-γ-lactone derivatives 1 and 3 was accomplished through lithium hydroxide mediated SN2 displacements in dimesylate 7, or more expeditiously, via trimesylate 21 through alkaline H2O2 mediated cleavage. [Copyright &y& Elsevier]

Abstract: A new reaction of diazomethane with norbornyl α-diketones in MeOH as solvent leading regioselectively to ketals is described. The mechanistic details of this intriguing reaction were investigated employing d 4-MeOH, EtOH and d 6-EtOH. The surprising observation of complete deuterium incorporation in the diazomethane-derived methoxy group was accounted for by sequential deuterium exchange between the initially formed hemiketal d 4-18 and diazomethane in the presence of d 4-MeOH as solvent. [Copyright &y& Elsevier]

Knoevenagel condensation proceeds efficiently in recyclable [bmim]PF6 and [bmim]BF4 without any catalyst, and hydrotalcites in ionic liquid serve as a safe and recyclable reaction system for both Knoevenagel as well as nitroaldol condensations. [Copyright &y& Elsevier]

Nitroarenes were chemoselectively reduced to the corresponding amines using zinc and aqueous ammonium salts in ionic liquids as a safe and recyclable reaction medium. Our results specify the effect of ammonium salts in the process; the combination of Zn/NH4Cl in [bmim][PF6] or Zn/HCO2NH4 in [bmim][BF4] were the suitable conditions for the reduction of nitroarenes. Azobenzenes were also smoothly reduced to hydrazobenzenes with Zn/HCO2NH4 (aq.) in recyclable [bmim][BF4] without any over reduction to the corresponding anilines. [Copyright &y& Elsevier]

• FeCl 3 catalyzed C C, C N bond formation between methyl enol ethers and anilines. • 2,3-Disubstituted indole formation via aryl group migration. • Anilines act as bis-nucleophiles. An intermolecular FeCl 3 catalyzed reaction between anilines and enol ethers is described. A variety of enol ethers and aromatic amines undergo a C C bond formation followed by cyclization via C N bond formation to afford the 2,3-disubstituted indoles, involving an unexpected aryl group migration. In this methodology, anilines act as bis-nucleophiles, wherein the initial attack occurs at the α-position of enol ether from the ortho position of aniline followed by the subsequent reaction of the amine moiety of aniline at the β-position, leading to the indole framework. This method is simple, obviates the use of expensive/hazardous transition-metal catalysts, and offers a wide range of substrate scope. [ABSTRACT FROM AUTHOR]

Abstract: A two-step synthesis of marine origin brominated alkaloids wilsoniamines A (1) and B (2), isolated from Australian bryozoan Amathia wilsoni Kirkpatrick, possessing a novel hexahydro-1H-pyrrolo[1,2-c]imidazol-1-one ring system is described. The core hexahydro-1H-pyrrolo[1,2-c]imidazol-1-one ring systems is constructed through a condensation reaction between (2,4,6-tribromo-3-methoxyphenyl)acetaldehyde and (S)-N-methylpyrrolidine-2-carboxamide as key steps. The orientation of substituted benzyl side-chain in the two epimeric natural products was controlled by carrying out the key condensation reaction under kinetic or thermodynamic conditions. [Copyright &y& Elsevier]

Abstract: A simple protocol for the synthesis of an aesthetically pleasing ‘oxa-basket’ (5-methoxy-2,8,13-trioxapentacyclo[7.2.1.1.5,120.4,1106,10]tridecane-3,7-dione), possessing 9-oxa-noradamantane core, is described. The readily available diquinane based dichloro bis-γ-lactone precursor upon treatment with MeSO3H furnished dichloro ‘oxa-basket’ which was dechlorinated using TBTH/AIBN to obtain the title compound. The key role of the chlorines was demonstrated by replacement with hydrogen or allyl substituents which redirects the cascade to simple hydrolysis products. [Copyright &y& Elsevier]

Abstract: A simple and useful protocol for the reduction of nitro arenes to their corresponding azoxy derivatives by employing zinc and NH4Cl in a mixture of [bmim][BF4] and water is described. The selective reduction of nitro to azoxy is attributed to the hitherto unknown moderating effect of oxygen on zinc metal. [Copyright &y& Elsevier]

Abstract: Synthesis of a compound with bowl-like, symmetrical molecular architecture, starting from a Diels–Alder adduct 7, derived from a reaction between 2,5-dihydro-2,5-dimethoxyfuran and 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene, is reported. [Copyright &y& Elsevier]

• Brønsted acid-induced one-pot synthesis of 2-methylbenzofurans. • Construction of new C–O bond formation via an efficient Grob-type fragmentation. • Halobenzofurans were successfully utilized to synthesis 6,7-bisaryl benzofurans. An efficient Brønsted acid-induced one-pot syntheses of 2-methylbenzofurans from norbornyl derivatives have been reported. The construction of new C–O bond proceeds via Grob-type fragmentation followed by cyclization and aromatization respectively. This synthetic strategy facilitates the efficient synthesis of 2-methylbenzofurans under acidic conditions. Significantly, this methodology is successfully applied to the synthesis of 6,7-bisaryl benzofurans. [ABSTRACT FROM AUTHOR]

• Acid mediated synthesis of thiazolines and enamide derivatives from methyl enol ethers. • Enol ethers acts as an electrophile. • C–N and C–S bond formation was achieved. • Application towards wilsoniamine B alkaloid. An efficient metal-free synthesis of thiazolines, dihydrothiazole and enureas or thioureas from methyl enol ether with urea or thiourea derivatives in the presence of TFA (trifluoroacetic acid) are reported here. This synthetic protocol involves the formation of two bonds, C–N as well as C–S, in one step for the synthesis of thiazoline derivatives, dihydrothiazoles and a direct C–N bond for the synthesis of enamides with good to excellent yields. Further, this method was employed for the synthesis of wilsoniamine B alkaloid. [ABSTRACT FROM AUTHOR]

Abstract: A concise stereoselective route to (±)-pentenomycin 1 in 33% overall yield starting from the readily accessible Diels–Alder adduct 4 is reported. The key reaction involves decarbonylation of β-methoxy-α,β-unsaturated aldehyde 8 obtained from β-hydroxy-dimethylketal 6. [Copyright &y& Elsevier]

• Total synthesis of (±) aspidostomide B, C and regioisomeric N -methyl aspidostomide is reported. • An unusual Lewis acid-mediated regioselective epoxide opening is described. • Aspidostomide B, C was achieved in six steps with overall yields of 54.7 and 59.0% respectively. A full account of the total synthesis of aspidostomide B, C, their analogues and our synthetic efforts towards the synthesis of aspidostomide D, which led to the synthesis of regioisomeric N -methyl aspidostomide D, its analogues via epoxide opening strategy is presented. The synthesis of regioisomeric N -methyl aspidostomide D involves an efficient, five-step sequence, with 36.3% overall yield, starting from 3,4,5-tribromo-1H-pyrrole-2-carboxylic acid. The key features of this protocol are intramolecular cyclization, dehydration, oxidation, and a Lewis acid-mediated regioselective epoxide ring opening by C-3 position of 2,5-dibromo-1H-indole to furnish the title compounds. [ABSTRACT FROM AUTHOR]

A regioselective synthesis of carbazole analogs belonging to both the categories of natural origin, viz., microorganisms and higher plant source is reported. The synthesis of carbazole derivatives possessing a methylester group at C-1 position has been achieved by Cadogan cyclization of nitro bi-phenyl derivatives, whereas, the carbazole analog possessing a methylester group at C-3 position was synthesized by Buchwald–Hartwig Pd-catalyzed cyclization of amino bi-phenyl derivatives. Suitably substituted bi-phenyl precursors were accessed from norbornyl α-diketones via Grob fragmentation, O-methylation and DBU aromatization reaction sequence. The reported carbazole derivatives possess structural features that are common with many carbazole natural products: mukonine, clausine-L, murrayafoline-A, and their sibling natural products. [ABSTRACT FROM AUTHOR]