Kinetika i mehanizam fenilselenoeterifikacije (Z)- i (E)-heks-4-en-1-ola [thesis]

Vera Divac
18-21 OTf Схема 7. У табели 1 су приказани резултати овог истраживања на серији хомоалилних алкохола (10-13) код којих jе дошло до затварања прстена 5endo-процесом. Сам стереохемијски пут реакције циклизације са реагенсом 9 је потпуно исти као и у реакцији интермолекулске метоксиселенације са поменутим реагенсом. 29b У производу 18 је установљено да је конфигурација новонасталог хиралног центра на С(2)-атому, (R)-конфигурације, што одговара нападу електрофила са re-стране двоструке везе
more » ... струке везе супстрата. Насупрот њему, нађено је да стереохемија производа 19 одговара нападу реагенса са si-стране. Прорачунима је установљено да интермедијерни селенонијум-јон производа 18 вероватно има структуру 26 29b (слика 5), где након anti-напада нуклеофила на овакав јон долази до формирања производа (R,R)-стереохемије. Abstract An innovative route for intramolecular cyclization of alkenols has been delineated through a ring closing reaction of suitably alkenols functionalized cyclic ethers tetrahydropyran or tetrahydrofuran type by reaction with phenylselenyl halides, in good yield. Proper choice of some 4and 5 -alkenols and pyridine as catalyst enables fast and facile cyclization. Catalytic amount of pyridine increased the yield, but in the presence of equimolar amount of pyridine, formation of corresponding cyclic ethers were quantitative and reaction were achieved instantaneously under extremely mild experimental conditions. It is possible that aromatic-aromatic ring stacking provides such role of pyridine. The effect of the steric hindrance in the starting alkenols, and halide ion of the selenenylating reagent is not significant, all halides generally giving equal results, and primary, secondary, tertiary and more substituted alkenols also giving quantitative yields. Abstract A fast and efficient method for intramolecular heterocyclization of (Z)-and (E)-hex-4-en-1-ols was developed. The method does not cause side reactions of the substrates and provides the cyclic phenylselenoethers in high yields after only few minutes. A catalytic amount of SnCl 2 increased the yield, but in the presence of an equimolar amount of SnCl 2 ,f o rmation of corresponding cyclic ethers were almost quantitative and reaction occurred instantaneously under extremely mild experimental conditions. Abstract: D 4 -Primary alkenols (Z)-and (E)-hex-4-en-1-ols underwent facile cyclization to the corresponding phenyl selenoethers using PhSeX (X = Cl, Br) in high yields and in good to excellent selectivities in the presence of some catalysts (Lewis acids and bases). The reaction succeeded in complete control of stereo-and regioselectivity. The best results were obtained with triethylamine and tin(II) chloride. Triethylamine as an additive in the reaction with (Z)-hex-4-en-1-ol gives only erythro-2-[1-(phenylseleno)ethyl]tetrahydrofuran, while the E-isomer gives cis-2-methyl-3-(phenylseleno)tetrahydropyran in large excess. Tin(II) chloride as an additive in the reaction with (Z)-hex-4-en-1-ol gives threo-2-[1-(phenylseleno)ethyl]tetrahydrofuran and with the E-isomer gives trans-2-methyl-3-(phenylseleno)tetrahydropyran. The reactions were performed under very mild experimental conditions, and the obtained yields were almost quantitative.
doi:10.2298/kg20130924divac fatcat:4kcg6xa6grdy7hkz32xb7a672u