Laccase-generated quinones in naphthoquinone synthesis via Diels-Alder reaction

The tandem synthesis of naphthoquinones was conducted from the reaction of laccase-generated quinones and acyclic dienes via Diels-Alder reaction. This reaction was carried out under mild condition in aqueous medium and yielded naphthoquinones up to 80%. In addition, the effect of solvent was also investigated and water was shown to be optimal for this reaction.     

Palladium-catalyzed synthesis of cyclopentane-fused benzocyclobutenes via tandem directed carbopalladation/C-H bond functionalization

A new Pd-catalyzed reaction for the stereoselective synthesis of cyclopentane-fused benzocyclobutenes is described. These transformations likely proceed via carbamate-directed carbopalladation followed by intramolecular C-H activation of an alkylpalladium intermediate. The mechanistic relationship between these transformations and Pd-catalyzed reactions of gamma-(n-Boc-amino)alkenes with aryl bromides that afford pyrrolidines is discussed. Differences in reactivity between Pd-amino and Pd-amido complexes appear to play a key role in the outcome of these transformations.     

Studies directed towards the stereoselective total synthesis of ilexlactone via a tandem ring-closing enyne metathesis protocol

Studies directed towards the stereoselective total synthesis of ilexlactone resulted in the synthesis of bicyclic systems 1a, 1b and ent-1a through tandem ring-closing enyne metathesis using Grubbs’ catalyst. The structures of synthetic 1a, 1b and ent-1a revealed that the proposed structure for ilexlactone is incorrect.     

A novel route to the marasmane skeleton via a tandem rearrangement-cyclopropanation reaction. total synthesis of (+)-isovelleral

A general and efficient route to the marasmane skeleton is described. Total syntheses of two simple marasmanes (35 and 37) in racemic form were achieved using a MgI2-catalyzed rearrangement-cyclopropanation reaction of trimethylsilyl enol ether 31 derived from naphthalenone 30. The reaction proceeds in high yield with complete diastereoselectivity and does not require the use of special cyclopropanation reagents. Application of this novel route to the marasmane framework was extended to the synthesis of naturally occurring (+)-isovelleral (41).     

Quinoxaline synthesis in novel tandem one-pot protocol

A variety of quinoxalines were synthesized via tandem one-pot procedure for the first time in water medium. The key strategy was the in situ preparation of α-halo-β-keto esters by the reaction of N-bromo succinimide with β-keto esters and further condensation with phenylene diamines. This novel eco-friendly approach offers an easy, efficient, and mild synthesis of highly substituted quinoxalines in good yields.     

A facile tandem protocol for the regioselective synthesis of novel thienobenzothiazepines

A series of new 3-benzyl-1,10-diaryl-4H,10H-thieno[3,4-c][1,5]benzothiazepines has been synthesised regioselectively from the reaction of 5-aryl-2,4-bis(arylmethylidene)dihydro-3-thiophenones with o-aminothiophenol in the presence of acetic acid. This transformation presumably occurs via a tandem Michael addition-condensation-isomerisation sequence.     

Tandem directed lithiations of N-Boc-1,2-dihydropyridines toward highly functionalized 2,3-dihydro-4-pyridones

[chemical reaction: see text]. Sequential tandem directed lithiations of an N-Boc-4-methoxy-1,2-dihydropyridine have been achieved, leading to C-5,C-6 disubstituted dihydropyridones on acidic workup. The chlorine atom of the dihydropyridone products can in turn be substituted giving rise to diverse substituents at C-6.     

A novel synthesis of 1,3,5-trisubstituted pyrazoles through a spiro-pyrazoline intermediate via a tandem 1,3-dipolar cycloaddition/elimination

The syntheses of an important class of hitherto unreported 1,3,5-pyrazoles, inspired by an unanticipated eliminatory ring opening are described. The reported pyrazole compounds were constructed through the Huisgen cyclization of 2-methylene-1,3,3-trimethylindoline and an in situ generated nitrile imine. The newly formed spiro-pyrazoline intermediate presumably then undergoes a ring opening/elimination process to afford a pyrazole, as evidenced by single X-ray crystal data. The current report constitutes the first formal observation of this kind of ring opening involving a spiro-pyrazoline intermediate.     

A novel one-pot pyrrole synthesis via a coupling-isomerization-Stetter-Paal-Knorr sequence

[reaction: see text]. 1,2,3,5-tetrasubstituted pyrroles can be synthesized in good yields in a one-pot, three-step, four-component process by a coupling-isomerization-Stetter reaction-Paal-Knorr sequence of an electron-poor (hetero)aryl halide, a terminal propargyl alcohol, an aldehyde, and a primary amine. The structures of the 1,4-diketone 4f and the pyrrole 6b were additionally supported by X-ray structure analyses.     

A novel synthesis of quinolinium salts via benzotriazole methodology

A novel method for the synthesis of 1,4- and 1,3,4-substituted quinolinium salts and 1,2,4- and 1,2,3,4-substituted-1,2-dibydroquinolines from N-substituted-N(benzotriazol-1-ylmethyl)aniline derivatives is reported.     

A novel synthesis of tetrahydrofuran via alkoxy radical cyclisation

Tetrahydrofurans were synthesised via 5-exo-trig cyclisation of alkoxy radical generated by unprecedented 1,5-hydrogen shift from hydroxyl group to vinyl radical.     

A stereoselective formal total synthesis of (+)-hyperaspine via a tandem aza-Michael reaction

A stereoselective formal total synthesis of (+)-hyperaspine via a tandem aza-Michael reaction as the key step in good yield is reported.     

A concise total synthesis of biologically active frutinones via tributylphosphine-catalyzed tandem acyl transfer-cyclization

A concise and step-economical total synthesis of biologically active frutinones has been achieved. Tributylphosphine (PBu₃) efficiently induced the tandem acyl transfer-cyclization of carbonates 5 to afford 3-methoxycarbonylflavone derivatives 4 in excellent yields. Finally, concomitant deprotection and lactonization under acidic conditions furnished the desired frutinones A (1a), B (1b), and the proposed structure of frutinone C (1c).     

A novel synthesis of fluorinated pyrazoles via gold(I)-catalyzed tandem aminofluorination of alkynes in the presence of Selectfluor

A mild and efficient protocol for the synthesis of fluorinated pyrazoles has been developed via gold(I)-catalyzed tandem aminofluorination of alkynes in the presence of Selectfluor. This method offers a broad substrate scope.     

A novel four-component tandem protocol for the stereoselective synthesis of highly functionalised thiazoles

The reaction of bis(aroylmethyl) sulfides with aromatic aldehydes and ammonium acetate in 1:2:1 molar ratio under solvent-free microwave irradiation afforded predominantly a series of thiazoles, viz., 1-aryl-2-[5(Z)-5-arylmethylidene-2,4-diaryl-2,5-dihydrothiazol-2-yl]ethanones stereoselectively. This reaction presumably occurs via a Knoevenagel condensation-Michael addition-cyclocondensation-ring opening-ring closing Michael addition sequence. The intermediacy of (Z,Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) in the above transformation is demonstrated by their conversion to the thiazoles upon reaction with ammonium acetate under solvent-free microwave irradiation.     

A novel practical synthesis of benzothiazoles via Pd-catalyzed thiol cross-coupling

A convenient synthesis of substituted benzothiazoles from 2-bromoanilides has been accomplished. The various 2-bromoanilides were reacted with an alkyl thiolate in high yields using a palladium catalyst. The resulting sulfides were easily converted to the corresponding benzothiazoles via the simultaneous generation of thiols and condensation under basic or acidic conditions.     

A novel synthesis of guanine PDE inhibitors via tricyclic imidazopyrimidines

A new method for the preparation of developmental tetracyclic guanine PDE inhibitors via a common tricyclic pyrimidine intermediate is described.     

A novel synthesis of chiral rotaxanes via covalent bond formation

Chiral rotaxanes composed of the asymmetric crownophane incorporating two hydroxy groups as a rotor moiety and the asymmetric axis were effectively synthesized via covalent bond formation, i.e. tandem Claisen rearrangement, esterification, and aminolysis.