A novel strategy for the synthesis of medium-sized lactams

[reaction: see text] A novel method for the synthesis of medium-sized lactams based on an auxiliary-mediated combined tethered/templated strategy is presented. Cyclization by a tethered ring-closing metathesis reaction was followed by a templated transannular aminolysis reaction to give seven- to ten-membered lactams in good yields.     

A regioselective 1,3-dipolar cycloaddition for the synthesis of novel spiro-chromene thiadiazole derivatives

A variety of 4′-(4-R-phenyl)-4-(methylthio)-2′-phenyl-2′H-spiro[chromene-2,5′-[1,2,3]thiadiazole] 5a–d and 5′-(4-R-phenyl)-4-(methylthio)-3′-phenyl-3′H-spiro[chromene-2,2′-[1,3,4]thiadiazole] 6a–d were synthesized regioselectively through the reaction of 4-(methylthio)-2H-chromene-2-thione 2 with diarylnitrilimines under refluxing dry chloroform. Whilst the reaction of 4-(allylthio)-2H-chromene-2-thione 3 with diarylnitrilimines under similar reaction conditions afforded the corresponding 4-(allylthio)-5′-(4-R-phenyl)-3′-phenyl-3′H-spiro[chromene-2,2′-[1,3,4]thiadiazole] 7a–d and 5-(4-R-phenyl)-2′-methyl-3-phenyl-2′,3′-dihydro-3H-spiro[[1,3,4]thiadiazole-2,4′-thieno[3,2-c]chromene] 9a–d as two unisolable diastereoisomeric forms. The structures of the obtained spiro cycloadduct thiadiazoles have been assigned by means of spectroscopic measurements.     

A novel strategy to the synthesis of 4-anilinoquinazoline derivatives

A novel approach to prepare 4-anilinoquinazoline derivatives based on the transformation of indoline-2,3-dione to formamidine was developed. The processes with this approach are simple, efficient, and environmentally friendly. The efficiency of this approach was evaluated by synthesizing 17 4-anilinoquinazolines and comparing the obtained yields with those achievable through conventional synthetic methods. It was the first time that compounds 8d, 8e, 8h, and 13b–f were synthesized. The characteristics of the IR and the UV spectra of these compounds and the effects of their substituents on the spectra were observed.     

A novel strategy for synthesis of multiblock copolymers

Multi-block copolymers with well-controlled numbers of blocks and block chain length are synthesized for the first time using a 'polyinitiator'.     

A novel degradative strategy for the synthesis of p-quinones.

p-Hydroxybenzylalcohols undergo Fremy's salt promoted degradative oxidation to give the corresponding p-benzoquinones. A novel strategy for the synthesis of p-benzoquinones based on the regioselective metalation of 2-methoxy-4-methoxymethyl phenols is presented.     

A novel strategy for the solid-phase synthesis of cyclic lipodepsipeptides

A rapid and efficient Fmoc solid-phase synthesis of cyclic lipodepsipeptide analogue 1 to antibiotic fusaricidin A is described. Our synthetic approach includes resin attachment of the first amino acid via side chain, successful use of combination of four quasi-orthogonal removable protecting groups, stepwise solid-phase synthesis of linear peptide analogue, lipid tail attachment followed by depsipeptide bond formation and on-resin head-to-tail cyclization. Undesired O→N acyl shift, which may occur during Fmoc removal, was successfully avoided by the incorporation of the lipid tail into the linear peptide precursor prior to on-resin depsipeptide bond formation and the ring closure.     

A novel strategy for the asymmetric synthesis of chiral cyclopropane carboxaldehydes

A new way of combining chiral auxiliaries and substrate-directable reactions for asymmetric synthesis is described that employs a three-step sequence of aldol-cyclopropanation-retro-aldol reactions for the stereoselective synthesis of enantiopure cyclopropane carboxaldehydes.     

The cycloaddition strategy for the synthesis of natural products containing carbocyclic seven-membered rings

Highly substituted carbocyclic seven-membered rings are frequently found in natural products and their synthesis represents a significant challenge to the synthetic chemist. Direct intramolecular cyclization of these systems often proves difficult and this fact has catalyzed the development of a variety of strategies based on a convergent intermolecular cycloaddition strategy. This concept article discusses the major cycloaddition approaches utilized to access these types of structures and primarily focuses on examples employed in the synthesis of natural products.     

A biomimetic synthesis of polycyclic quinones

Various polycyclic quinones were synthesized by the intramolecular condensation of polyketides followed by the air-oxidation.     

Intramolecular 1,3-dipolar cycloaddition strategy for enantioselective synthesis of FR-900482 analogues

[reaction: see text] Enantioselective synthesis of FR-900482 analogues is described. The key reaction of the synthesis is intramolecular 1,3-dipolar cycloaddition of a highly functionalized nitrile oxide with complete stereo- and regioselectivities to construct the eight-membered benzazocine ring.     

Exploring azide-enolate cycloaddition in the synthesis of novel Rufinamide analogs

The exploration of azide-enolate cycloaddition in the synthesis of novel Rufinamide analogs is reported for the first time. A very simple procedure involving the use of β-ketonitriles as dipolarophiles afforded 5-aril/heteroayl Rufinamide derivatives in two steps.     

A novel strategy for bioconjugation: synthesis and preliminary evaluation with amphotericin B

A novel linker strategy is presented based on a double reductive amination of a dialdehyde to the amine of the amphotericin B mycosamine sugar and the biological activity of a series of conjugates is compared to the native amphotericin B.     

Anionic [4+2] cycloaddition strategy in the regiospecific synthesis of carbazoles: formal synthesis of ellipticine and murrayaquinone A

Anionic [4+2] cycloaddition of furoindolones (e.g., 7 and 10) has been developed as an effective means to the synthesis of carbazoles. This reaction has been shown to be feasible with a wide variety of Michael acceptors to give carbazoles and fused carbazoles in good yields. The scope and limitations of the reaction have been briefly studied. The nature of N-protection of the furoindolones (cf. 7) plays a major role in the success of annulation.     

Iptycene quinones: synthesis and structure

A practical and efficient method to synthesize iptycene quinones has been developed. As a result, a series of pentiptycene quinones 8-16 were conveniently synthesized by one-pot reaction of triptycene quinone 4 or 5 with anthracene 1 or its derivatives 2-3 in refluxing acetic acid in the presence of p-chloranil, followed by CAN oxidative demethylation. Similarly, a series of heptiptycene quinones 17-23 with U-shaped cavities were achieved with pentiptycene quinone 10 and triptycene diquinone 6 as precursors. Non-iptycene triquinones 24 with one tweezer-shaped cavity and 25 with two U-shaped cavities were synthesized by one-pot reactions of anthracene with pentiptycene triquinones 16a and 16b, respectively. Non-iptycene triquinone 26 with a dendritic structure was conveniently obtained by the reaction of anthracene with either pentiptycene diquinone 12 or triptycene triquinone 7. The structures of regioisomers 16a and 16b were determined by the single-crystal structure analysis of 16b. The structures of other regioisomers, including heptiptycene tetraquinones 19a/19b/19c and heptiptycene triquinones 23a/23b, were identified by comparative reactions.     

A novel strategy for oligopeptide synthesis using a polymer-supported ammonium fluoride

A novel method for the preparation of oligopeptides with a PS-ammonium fluoride in the solution phase is reported. The synthesis of lipid II pentapeptide is efficiently synthesized via a PS-ammonium fluoride without chromatographic purifications. The method reported here is very convenient to synthesize a relatively large amount of oligopeptides with abundantly available Fmoc-protected amino acids in a time efficient manner.     

Toward a total synthesis of the stemofoline alkaloids: Advancement of a 1,3-dipolar cycloaddition strategy

Novel, intramolecular 1,3-dipolar cycloadditions of azomethine ylides have been applied to the synthesis of functionalized core structures of the stemofoline alkaloids. In an effort to maximize the efficiency of this key transformation in the context of an eventual total synthesis of these complex natural products, a number of strategic modifications to the cycloaddition substrate were investigated. The collective efforts have provided useful insights into the operative, regiochemical control elements for 1,3-dipolar cycloadditions leading to stemofoline alkaloids. A potential intermediate in the synthesis of these alkaloids was prepared.