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صفحه اصلی
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بیست و نهمین کنفرانس شیمی آلی ایران
Mechanism and Periselectivity of the higher-order Cycloaddition reactions of Azaheptafulvenes within the Molecular Electron Density Theory
نویسندگان :
Mina Haghdadi ( دانشگاه ازاد بابل ) , Mahshid Hamzehlouian ( دانشگاه ازاد جویبار ) , Houra Kabirnataj ( دانشگاه ازاد ساری )
کلید واژه ها :
Mechanism،periselectivity،azaheptafulvenes،high-order cycloaddition
چکیده مقاله :
The competition among thermally allowed [4+2], [6+4], and [8+2] cycloaddition reactions has prompted much investigation. Cycloaddition reactions involving more than six π electrons are termed higher-order cycloadditions.[1] The origins of periselectivity of higher-order cycloadditions are poorly understood. The cycloaddition reactions of 8-(p-Chlorophenyl)-8-azaheptafulvene with various fulvenes, which reported by Liu et al., give [6+2] and [4+2] cycloadducts, depending on the substituents present on the fulvene. [2] The highly peri-, regio- and stereoselective cycloaddition of 8-azaheptafulvene to disubstituted fulvenes renders these reactions an interesting platform upon which to investigate origins of periselectivity in higher-order cycloaddition reactions. We have now used density functional theory calculations to explore the entire reaction pathway, with a focus on the selectivities of the cycloaddition reactions of Liue experiments. The mechanism and origins of stereoselectivity were explained using the M06-2X density functional. The stereoisomeric transition states are distinguished by the steric interactions between the R groups of the fulvene to the C- methine group of the 8-azaheptafulvene. Increasing steric bulk of the larger one of the two exocyclic substituents on the fulvenes should cause higher periselectivity, and thus the reaction of fulvene with 8-azaheptafulvene took place exclusively on the endocyclic double bond that is anti to the larger exocyclic substituent of the fulvene. All results show that the exocyclic substituent effects exert controlling influence upon the periselectivity and regioselectivity of these cycloadditions.
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