Yan-Chao Wu

Rearrangement of Dypnones to 1,3,5-Triarylbenzenes

Rearrangement of dypnones to 1,3,5-triarylbenzenes is described. The reaction is proposed to involve an aldol-type self-condensation of dypnones, followed by an intramolecular [2 + 2] cycloaddition and a retro-[2 + 2] cycloaddition. The reaction goes smoothly under obviously milder conditions in comparison to the cyclotrimerization of acetophenones to 1,3,5-triarylbenzenes (10 mol % of TsOH, 80 °C versus 130-148 °C). This unexpected rearrangement would provide new possible considerations in dypnone-involved organic synthesis.

Cascade reaction of β,γ-unsaturated α-ketoesters with phenols in trityl chloride/TFA system. Highly selective synthesis of 4-aryl-2H-chromenes and their applications

The treatment of β,γ-unsaturated α-ketoesters with phenols in the presence of trityl chloride and 4 Å molecular sieves in refluxing trifluoroacetic acid afforded 4-aryl-2H-chromenes in high yields, in which a reverse of the regiochemistry of Jørgensen-Rutjes chromane synthesis was observed. The isolation of 4H-chromene intermediates, confirmed by single-crystal X-ray analysis, indicates that the early stage of the reaction involves a Friedel-Crafts alkylation/cyclodehydration processes. Stirring of the 4H-chromene intermediate with trityl chloride in deuterotrifluoroacetic acid under reflux afforded the 2H-chromene and triphenylmethane in high yields, which implies the late stage of the reaction involves a hydrogen transfer process. Highly selective derivation of the hydroxyl esters to the corresponding hydroxyl amides, amino acids, amino esters and Friedel-Crafts adducts was further accomplished. Our endeavors will lead to a better understanding of the controlling elements behind their structural motifs. The products were confirmed unambiguously from their spectra and by single-crystal X-ray analysis.

Mild and Efficient Allylation of Indoles and Amides Using Amberlyst-15 as a Recyclable Heterogeneous Catalyst

Abstract A mild and efficient allylation of indoles and amides in the presence of a catalytic amount of Amberlyst-15 has been described in this context. The recyclable heterogeneous catalytic system is practical and facile for the synthesis of C- and N-allylated derivatives and would be of importance for the development of the accordingly functional complex molecules. GRAPHICAL ABSTRACT

Regioselective 1,2-Diol Rearrangement by Controlling the Loading of BF3·Et2O and Its Application to the Synthesis of Related Nor-Sesquiterene- and Sesquiterene-Type Marine Natural Products

The regiocontrolled rearrangement of 1,2-diols has been achieved by controlling the loading of BF3·Et2O. Its applicability is showcased by the divergent synthesis of austrodoral, austrodoric acid, and 8-epi-11-nordriman-9-one, as well as a formal synthesis of siphonodictyal B and liphagal. A new light is shed on piancol-type rearrangements that will be useful in diversity-oriented synthesis of related natural products.

Synthesis of functional 4H-chromenes from phenols and acetophenones under solvent- and metal-free conditions

Sulfuric-acid-promoted tandem reaction of phenols with acetophenones under solvent- and metal-free conditions has been developed, which afforded functional 4H-chromenes in good yields with water as the side product. Sulfuric acid appeared to serve the dual role of an efficient promoter and a suitable dehydrating agent.

Water-promoted ortho-selective monohydroxymethylation of phenols in the NaBO2 system

Water-promoted ortho-selective monohydroxymethylation of phenols in the NaBO2 system generates salicyl alcohols in 65-97% yields. A remarkable rate-enhancement by water was observed, and NaBO2 appeared to serve the dual role of a suitable base and an efficient chelating reagent. This protocol possesses many advantages such as short reaction times, expanded substrate scope, and high mono- and regio-selectivities. The experimental results were explained by the calculations based on local ionisation energy minima, leading to a possible reaction mechanism.

Protecting-group-free synthesis of haterumadienone- and puupehenone-type marine natural products

A divergent and expeditious access to haterumadienone- and puupehenone-type marine natural products has been achieved by using a newly developed hemiacetalization/dehydroxylation/hydroxylation/retro-hemiacetalization tandem reaction as one of the key steps. Its applicability is showcased by the first synthesis of haterumadienone, 20-hydroxyhaterumadienone, 20-epihydroxy-haterumadienone and 20-acetoxy-haterumadienone, as well as the facile synthesis of puupehenone, puupehedione and puupehenol. The synthesis is efficient, and atom- and step-economical (6 to 9 steps from commercially available starting materials), and requires no protecting groups and transition metals.

Enantiospecific Semisynthesis of Puupehedione-Type Marine Natural Products

An enantiospecific semisynthesis of puupehedione was achieved from sclareolide in only 7 steps with an overall yield of 25%. The key drimanal trimethoxystyrene skeleton was constructed by the palladium-catalyzed cross-coupling reaction of an aryl iodine and a drimanal hydrazone. An in situ CAN-oxidation/intramolecular oxa-Stork-Danheiser transposition tandem reaction was used as a powerful tool to install concurrently the C and D rings of puupehedione in a one-pot fashion. Its applicability was also showcased by the semisynthesis of puupehenone and puupehenol.

Synthetic Studies on Potent Marine Drugs: Synthesis and the Crystal Structure of 6-tert-butyl-4-phenyl-4H-chromene-2-carboxylic Acid

4H-Chromene-2-carboxylic acid ester derivatives of renieramycin M might be of use for the structural-activity relationship studies of antitumor antibiotic tetrahydroisoquinoline natural products. Accordingly, 6-tert-butyl-4-phenyl-4H-chromene-2-carboxylic acid, one key intermediate, was synthesized via the condensation of (3E)-2-oxo-4-phenylbut-3-enoate methyl ester with 4-tert-butylphenol in the presence of AuCl3/3AgOTf (5 mol%), followed by cyclodehydration and aqueous hydrolysis. The product was unambiguously shown to the 4H-chromene-2-carboxylic acid by spectroscopy and X-ray crystallographic analysis. A packing diagram of the crystal structure shows that aromatic -stacking interactions and O–H⋯O hydrogen bond stabilize the structure in the solid.

Gravimetric, electrochemical and surface studies on the anticorrosive properties of 1-(2-pyridyl)-2-thiourea and 2-(imidazol-2-yl)-pyridine for mild steel in hydrochloric acid

1-(2-Pyridyl)-2-thiourea (TP) and 2-(imidazol-2-yl)-pyridine (IP) are described here for the first time as inhibitors of mild steel corrosion in acidic medium based on investigations such as weight loss tests, potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The experimental results revealed that 1-(2-pyridyl)-2-thiourea and 2-(imidazol-2-yl)-pyridine are effective corrosion inhibitors for mild steel in acidic medium, and their maximum corrosion inhibition efficiencies at 4 × 10−4 M are 93.57% and 96.66%, respectively. TP and IP are determined as mixed-type inhibitors based on polarization studies, and their adsorption on the mild steel surface follows the Langmuir adsorption isotherm and physical adsorption is dominant. The formation and characteristics of the protective layer on the steel surface were verified by scanning electrochemical microscopy (SECM), UV-visible spectroscopy, FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS) methods. Besides, the correlation between the inhibition efficiency and the molecular structure of inhibitors was theoretically studied via quantum chemical calculations.