| Attributs | Valeurs |
|---|
| type
| |
| Is Part Of
| |
| Subject
| |
| Title
| - Cycloaddition Reactions of a Nitrogen-Substituted Oxyallyl Cationwith Cyclopentadiene and Substituted Furans. ReactionConditions, Diastereoselectivity, Regioselectivity, andTransition State Modeling
|
| has manifestation of work
| |
| related by
| |
| Author
| |
| Abstract
| - An investigation of the cycloaddition reactions of anitrogen-substituted oxyallyl cation is presented.The nitrogen-substituted oxyallyl cation,M+-1 (M+ = H+ orLi+), can be generated from thedibromide 2 using eitherCF3CH2OH/Et3N orLiClO4/CH3CN/Et3N. Theseoxyallyl cations werefound to undergo [4 + 2] cycloaddition reactions with furan,cyclopentadiene, 2-methylfuran, and2-methoxyfuran. The diastereo- and regioselectivities in thesereactions were found to be positivelyinfluenced by the presence of Li+. Reaction ofM+-1 with the 2-substituted furans led toprimarilythose adducts arising from endo addition (as was observed with theunsubstituted dienes) andwhich had the 2-substituent syn to the bromine. Consideration ofthe frontier molecular orbitalsof the reacting species (Li+-1 and2-substituted furans calculated at the PM3 semiempiricallevelof theory) led to the conclusion that FMO theory does not explain theregiochemistry observed inthis process, although the relative electrophilicity ofM+-1 (M+ = H+ orLi+) could be rationalized.Transition structure modeling was consistent with empiricalobservations in that it predicted anendo addition of furan to Li+-1 via a stepwisereaction. Calculation of the reaction coordinate forthis nonconcerted process predicted a ΔHrxn∼ −50 kcals/mol and ΔHact ∼ +11kcal/mol, with thesecond bond-forming process having a ΔHact ∼+1.7 kcal/mol.
|
| article type
| |
| is part of this journal
| |
