Bencan Tang

Total synthesis of (+)-intricarene using a biogenetically patterned pathway from (−)-bipinnatin J, involving a novel transannular [5+2] (1,3-dipolar) cycloaddition

An asymmetric synthesis of the furanobutenolide-based macrocyclic diterpene (-)-bipinnatin J (4a) isolated from the gorgonian octocoral Pseudopterogorgonia bipinnata is described. The synthesis is based on elaboration of the chiral lactone-substituted vinyl iodide 26b from (+)-glycidol, followed by an intermolecular Stille coupling reaction with the stannylfurfural 27, leading to 28a, and then an intramolecular Nozaki-Hiyama-Kishi allylation reaction, 28b --> 4a. Treatment of (-)-bipinnatin J (4a) with VO(acac)2-tBuO2H followed by acetylation of the tautomeric hydroxypyranone product 7/8, next gave the acetoxypyrone 30. When the acetoxypyranone 30 was heated in acetonitrile in the presence of DBU, it gave (+)-intricarene 1, which is found in P. kallos, via a novel transannular [5+2] (or 1,3-dipolar) cycloaddition involving the butenolide-oxidopyrylium ion intermediate 31. We believe that this total synthesis of (+)-intricarene 1 mimics its most likely origin in nature via oxidation of (-)-bipinnatin J (4a), presumably involving photochemically generated singlet oxygen or possibly a P450 monooxygenase enzyme system.

Advances on transition metal oxides catalysts for formaldehyde oxidation: A review

ABSTRACT This article highlights recent advances in the development of transition metal-based catalysts for formaldehyde oxidation, particularly the enhancement of their catalytic activity for low-temperature oxidation. Various factors that enhance low-temperature activity are reviewed, such as morphology and tunnel structures, synthesis methods, specific surface area, amount and type of active surface oxygen species, oxidation state, and density of active sites are discussed. In addition, catalyst immobilization for practical air purification, reaction mechanism of formaldehyde oxidation, and the reaction parameters affecting the overall efficiency of the reaction are also reviewed.

Metal-free base-mediated oxidative annulation cascades to 3-substituted-3-hydroxyoxindole and its 3-spirocyclic derivative

A simple and efficient method was developed for the construction of the medicinally important 3-substituted-3-hydroxyoxindole and its 3-spirocyclic derivatives with readily available aniline derivatives as starting materials. This highly atom- and step-economical one-pot protocol was carried out under metal-free base-mediated conditions through a novel oxidative annulation strategy with oxygen as the oxidant. The key intermediates were isolated and confirmed. A reasonable reaction pathway was proposed and supported by the preliminary experiments, and the computational studies were carried out to understand the energetics of the key rearrangement reaction.

Advancement in knowledge of phenomena and processes: general discussion

Hongmin Zhu replied: We want to analyze the effect of F ion on the equilibrium of the titanium ions and metallic titanium. By adding F ion into a chloride molten salt, you can tune the coordination situation of anions around the cation. In molten salts each cation is always coordinated by some anions. When F ions are introduced into chloride salts, the F ions will be preferentially coordinated to the higher valance cations (in this case, Ti and Ti); this will drive the equilibrium of the disproportionation reaction to the higher valance cation side. Therefore, by analyzing carefully the effect of the F ion addition to the equilibrium, you will be able to know the relative stability (chemical potential) of the cations. This is also linked with the electrode reaction steps.