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Relevant academic research and scientific papers

Catalytic direct arylation with aryl chlorides, bromides, and iodides: Intramolecular studies leading to new intermolecular reactions

A catalyst for the intramolecular direct arylation of a broad range of simple and heterocyclic arenes with aryl iodides, bromides, and chlorides has been developed. These reactions occur in excellent yield and are highly selective. Studies with aryl iodides substrates revealed that catalyst poisoning occurs due to the accumulation of iodide in the reaction media. This can be overcome by the addition of silver salts which also permits these reactions to occur at lower temperature. The utility of the methodology is illustrated by a rapid synthesis of a carbazole natural product and by the synthesis of sterically encumbered tetra-ortho-substituted biaryls via ring-opening reactions of the direct arylation products. Mechanistic investigations have provided insight into the catalyst's mode of action and show the presence of a kinetically significant C-H bond cleavage in palladium-catalyzed direct arylation of simple arenes. Knowledge garnered from these studies has led to the development of new intermolecular arylation reactions with previously inaccessible arenes, opening the door for the development of other new direct arylation processes.

A novel method for the efficient synthesis of methyl 2-oxo-2- arylacetates and its application to the preparation of fungicidal methyl (E)- O-methyloximino-2-arylacetates and their (Z)-stereoisomers

Methyl 2-oxo-2-arylacetates 1, which include some fluorinated compounds, have been synthesized in moderate to excellent yields by reaction of methyl oxalyl chloride with arylzinc halides in the presence of Pd(PPh3)4. The highest yields have been obtained when these reactions involved arylzinc bromides which were prepared by conversion of the corresponding aryl bromides to organolithiums, followed by transmetallation with ZnBr2. Compounds 1 have been converted in high yields to the corresponding (E)- and (Z)-O- methyloximino-2-arylacetates (E)- and (Z)-5 by treatment with O- methylhydroxylamine hydrochloride in pyridine. Compounds (E)- and (Z)-5 have been easily separated by MPLC on silica gel and their structure and stereochemistry have been assigned by NMR techniques. So prepared compounds of general formula 5 included an agrochemically important fungicide, i.e. (E)-5c, its fluorinated structural analogues, as well as compounds which proved to be able to delay the growth of fungal species isolated from deteriorated papers. Interestingly, several compounds of general formula (Z)- 5 underwent partial stereomutation in the presence of daylight and catalytic amounts of iodine.