Syntheses of (-)-TAN-2483A, (-)-massarilactone B, and the fusidilactone B ring system. Revision of the structures of and syntheses of (+/-)-Waol A (FD-211) and (+/-)-Waol B (FD-212)

The structure of waol A has been revised from 1 to 6, the vinylogue of TAN-2483A (5). Aldol reaction of hydroxybutanolides 13b,c with 2,4-hexadienal affords 12b,c, which are subjected to iodoetherification with bis(sym-collidine)IPF6 to provide 11b(c). Treatment with Et3N in CH2Cl2 completes the three-step syntheses of TAN-2483A (5) and waol A (6). Aldol reaction of hydroxybutanolide 31 with 2,4-hexadienal affords 32, which is subjected to iodoetherification to provide 34, which in turn is treated with Bu3SnCl, NaBH3CN, and oxygen to provide diol 60. Further elaboration completes the first syntheses of massarilactone B (7) and the fusidilactone B (9) ring system.     

Reduction of nitric oxide,nitrous acid and nitrogen dioxide at platinum electrodes in acidic solutions: Review and new voltammetric results

The literature concerning the chemical and electrochemical reactions of nitric oxide, nitrous acid and nitrogen dioxide in aqueous solutions is reviewed briefly, with emphasis on electrochemical reductions at platinum electrodes in acidic solutions. The voltammetric behavior of NO and NO₂ at a Pt electrode in perchloric acid is virtually identical to that for HNO₂ and this is explained on the basis of a common electroactive precursor concluded to be NO⁺. Three cathodic waves are obtained for acidic solutions of NO, HNO₂ and NO₂. The first two waves correspond to reduction of NO⁺ to NO and N₂O₃ to NO, respectively. The presence of N₂O₃ results from decomposition of the parent compounds. The presence of Br^- or Cl^- in acidic solutions of the title compounds promotes the voltammetric reductions at lower H⁺ concentrations. This probably results from formation of electroactive nitrosyl halides.     

Total Synthesis of (+/-)-Leporin A

An efficient synthesis of (+/-)-leporin A (1) has been developed using a tandem Knoevenagel condensation-inverse electron demand intramolecular hetero Diels-Alder reaction to construct the key tricyclic intermediate 3 from pyridone 5 and dienal 6 in one pot in 35% yield. Hydroxylation (71%) of 3 and methylation (77%) of the resulting hydroxypyridone 2 completed the first total synthesis of (+/-)-leporin A (1).     

Polymerization of 4-vinylpyridinium salts. III. A clarification of the mechanism of spontaneous polymerization

The mechanism of the spontaneous polymerization of 4-vinylpyiridine on quaternization or protonation has been investigated. Results indicate that initiation is caused by the nucleophilic attack of 4-vinylpyridine on the double bond of 4-vinylpyridinium ion. It was shown that halide ions do not contribute significantly to the initiation. In the case of acid salts of 4-vinylpyridine a hydrogen-transfer polymerization occurred to give an ionene polymer with pyridinium units in the main chain. The “matrix” polymerization of 4-vinylpyridine on poly(phosphoric acid) or poly(acrylic acid) also resulted in ionene formation. Conditions under which stable 4-vinylpyridinium salts can be obtained are discussed.     

Model for diffusion-limited electrochemiluminescence

An approximate analytic expression is derived, based on a novel model for the reactive–diffusive processes in a electrochemiluminescence (ecl) experiment. The physical system treated is one in which ecl is produced by stepping the voltage of a planar electrode to the diffusion-limited reduction value for an emitter species in the presence of a bulk oxidant precursor (9,10-DPA with benzoyl peroxide). The unknown rate constants are determined by a least-squares curve-fitting computer code. The model, though crude, provides an excellent fit to the ecl intensity versus time data, including the rise portion of the curve.     

Copolymerization behavior of vinylimidazolium salts

Copolymerization studies of cationic monomers have been reported in the literature to yield wide variations in reactivity ratios and Q–e values, depending on the comonomer and the nature of the solvent. In this work are presented the copolymerization characteristics of a variety of vinylimidazolium salts in both water and ethanol solution. From these studies, the effect of solvent polarity, of substitution at the imidazolium 2-position, of the type of counterion, and of the hydrophilic–hydrophobic character of the monomeric salts could be ascertained. The results of the study are consistent with other related investigations, in that solvent polarity and comonomer both strongly affected copolymerization.     

Synthesis of the carbocyclic skeleton of abyssomicins C and D

[reaction: see text] Intramolecular Diels-Alder substrate trienyl methylenebutenolide 5 was prepared in six steps by coupling 3-methoxy-4-methylenebutenolide (6) with trienone keto aldehyde 7. Heating 5 in CHCl(3) for 2 d at 70 degrees C afforded 80% of a single Diels-Alder adduct 4 with the complete carbon skeleton of abyssomicin C. Addition of thiophenoxide to the enone double bond of 4 followed by an intramolecular Michael addition afforded 15 with the abyssomicin D carbon skeleton.     

Synthesis of (-)-dysiherbaine

[reaction: see text] The first synthesis of (-)-dysiherbaine has been accomplished using intramolecular SN2 substitutions of a carbamate anion on an epoxide and an alkoxide on a secondary mesylate to efficiently construct the bicyclic skeleton stereospecifically from xylose. A general sequence has been developed to introduce an allyl group and convert it to the alanine side chain that should be useful for the construction of dysiherbaine analogues.