Hypervalent iodine oxidation of phenol derivatives using a catalytic amount of 4-iodophenoxyacetic acid and Oxone as a co-oxidant

Reaction of p-substituted phenols 2 with a catalytic amount of 4-iodophenoxyacetic acid (1) and Oxone^® as a co-oxidant in tetrahydrofuran (THF) or 1,4-dioxane-water gave the corresponding p-quinols 3 in excellent yields. Reaction of p-dialkoxyarenes 4 in 2,2,2-trifluoroethanol-water gave the corresponding p-quinones 5 in excellent yield without purification. These reactions provide efficient and practical methods for the preparation of p-quinols and p-quinones from p-substituted phenols and p-dialkoxyarenes, respectively. This quinone synthesis was applied to synthesis of blattellaquinone (13), the sex pheromone of the German cockroach Blattella germanica.     

Reagent-controlled stereoselective synthesis of (±)-gallo- and (±)-epigallo-catechin gallates

Synthesis of (±)-gallocatechin and (±)-epigallocatechin gallates by electrophilic cycloarylation is reported. The precursors for cyclization were prepared by reagent-controlled stereo-selective opening of epoxide with phenol. Activation of the S-oxidized S,O-acetal enabled electrophilic cycloarylation to stereoselectively provide the acylated catechins.     

Practical and efficient synthesis of the (R)-atropisomer of a 4-phenyl 1,2,4-triazole derivative as a selective GlyT1 inhibitor

Herein we describe a novel and efficient method for synthesizing the (R)-atropisomer of 3-[3-ethyl-5-(6-phenylpyridin-3-yl)-4H-1,2,4-triazol-4-yl]-2-methylbenzonitrile 1, a novel GlyT1 inhibitor. The diastereomeric salt formation of 3-[3-ethyl-5-(6-phenylpyridin-3-yl)-4H-1,2,4-triazol-4-yl]-2-methylbenzoic acid 7 with (1R,2S)-(?)-2-amino-1,2-diphenylethanol afforded the desired (R)-atropisomer. We also report the determination of the absolute configuration of (R)-7 by powder X-ray diffraction.     

First synthesis and absolute configuration of (−)-pyriculariol, a phytotoxin isolated from rice blast fungus, Magnaporthe grisea. Use of microwave irradiation to control Stille coupling reaction products

First total synthesis of (−)-pyriculariol, a phytotoxin isolated from rice blast fungus, Magnaporthe grisea, was achieved to determine the absolute configuration of the natural product to be 5′R,6′S. The key step was Stille coupling reaction using microwave irradiation from −78 °C to control the reaction.     

Organocatalytic Enantioselective Decarboxylative Reaction of Malonic Acid Half Thioesters with Cyclic N‐Sulfonyl Ketimines by Using N‐Heteroarenesulfonyl Cinchona Alkaloid Amides

The organocatalytic enantioselective decarboxylative Mannich reaction of malonic acid half thioesters (MAHTs) with cyclic N‐sulfonyl ketimines by using N‐heteroarenesulfonyl cinchona alkaloid amides afforded products with high enantioselectivity. Both enantiomers of the products could be obtained by using pseudoenantiomeric chiral catalysts. The reaction proceeds through a nucleophilic addition of the MAHTs to the ketimines prior to decarboxylation.     

Chemo‐ and Regioselective Reduction of 5,15‐Diazaporphyrins Providing Antiaromatic Azaporphyrinoids

Reagent‐controlled chemo‐ and regioselective reduction of 5,15‐diazaporphyrins has been developed. The selective reduction of carbon–carbon double bonds of diazaporphyrins provides 18 π aromatic isobacteriochlorin‐type products, whereas the reduction of carbon–nitrogen double bonds leads to selective formation of 20 π N,N′‐dihydrodiazaporphyrins in excellent yields. The distinct antiaromatic character of N,N′‐dihydrodiazaporphyrins has been revealed. The free‐base N,N′‐dihydrodiazaporphyrin exhibits slower inner NH tautomerism than that in the corresponding 18 π porphyrins.     

Contamination by butyltin compounds in harbour porpoise (Phocoena phocoena) from the Black Sea

Concentrations of butyltin compounds (BTs) were determined in harbour porpoise (Phocoena phocoena) collected from the Turkish coastal waters of the Black Sea. Total butyltin compounds (∑ BTs) in the liver were in the range of 89–219 ng/g on a wet weight basis. The dibutyltin (DBT) residues were higher than those of tributyltin (TBT), suggesting the degradation of TBT to DBT in the liver and the metabolic capacity comparable to other marine mammals. Any sex difference and age-dependent accumulation of BTs residues were not found in harbour porpoises, but residue levels increased until maturity and then remained constant. When compared with other marine mammals, the present results indicate that the Black Sea is also contaminated with butyltin compounds, but to a lesser degree than coastal waters of developed nations. The biomagnification factor in harbour porpoises was 0.8, which was comparable with pinnipeds and lower than cetaceans. Received: 23 December 1996 / Revised: 15 April 1997 / Accepted: 16 April 1997