Furan 2- -4-chloro-, formation from

Phosphorus ylides can be generated from triphenylphosphine, 3-chloro-(3//, 5//)-furan-2,4-dione, and alkynyl esters. Additional alkynyl ester, acting as a Michael acceptor, reacts with the ylides in a [4+2] cycloaddition reaction that results in the formation of furo[2,3-3]pyran derivatives (Equation 30) <2000T5221>. 

As discussed in the earlier survey (1), a biogenic source of polychlorinated dibenzo-p-dioxins and dibenzofurans is peroxidase-catalyzed transformation of chlorophenols as first reported by Oberg and Rappe (2041-2044). More recent studies confirm these observations (2045-2048). In addition to lactoperoxidase and horseradish peroxidase, human leukocyte myeloperoxidase catalyzes in vitro formation of dioxins and dibenzofurans from chlorophenols (2046, 2047). Formation rates are in the pmol/mol range (Scheme 3.6) demonstrating that a human biosynthesis of dioxins and furans is not only possible but also likely. These observations are reinforced by the reported in vivo (rats) conversion of the pre-dioxin nona-chloro-2-phenoxyphenol to octachlorodibenzo-p-dioxin (OCDD) (2049), and the production of hepta- and octachlorodibenzo-p-dioxin in the feces of cows fed pentachlorophenol-treated wood (Scheme 3.7) (2050, 2051). 

Ethyl 3-aminofuropyridine-2-carboxylates were reported to be made either from 1-hydroxy-2-cyano-substituted pyridines and ethyl bromoacetate or from l-chloro-2-cyano-substituted pyridines and ethyl glycolate under microwave conditions <07S3247>. Microwave irradiation was also applied in the Rap-Stoermer reaction for the formation of benzo[A] furans from salicylaldehydes and diverse phenacyl bromides and phenacyl iodides... 

Furans are obtained a.s side-products during iodotrimethylsilane reduction of benzoins or by elimination of water after hemiacetal formation. Perlluoro(tetramethylfuran) 22 is synthesized by an unusual sequence starting from ketenimine 20. Treatment with 3-chloro-peroxybenzoic acid gives ketone 21, a compound that in an assumed radical process reacts W ith 0.6 equivalents of bromine at 250 C in a Pyrex ampule to form furan 22 in 95% yield. 

Eliminations. Alkenes are formed rapidly from v/c-dibromides, )3-chloro-ethers, jS-iodoethyl esters," and /3-acetoxy sulfones" on treatment with SmL. The formation of furan derivatives from epoxypropargyl esters by reaction with... 

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