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Semiempirical Calculations on Heterodiene-Heterocumulene Cycloadditions

Walter M. F. Fabian ; Institut fiir Organische Chcmie, Karl-Franzcns-Univcristat Graz, Austria
Gert Kollenz ; Institut fiir Organische Chcmie, Karl-Franzcns-Univcristat Graz, Austria

Puni tekst: engleski pdf 24.017 Kb

str. 55-67

preuzimanja: 295



4-Benzoyl substituted five-membered heterocyclic 2,3-diones (e.g. furan- diones or pyrrolcdiones) add various hclcrocumulcncs giving bicyclic hctcro- cyclcs. The structures of the products obtained in these reactions can be rationalized by assuming an initial [4 + 2] cycloaddition between the heterodiene system formed from the benzoyl group and the cndocyclic C = C double bond of the heterocyclic ring and the hctcrocumulcnc, followed by special and novel furandione rearrangements. Although some formal [4 + 2] cycloadditions of kctcncs are known, their reactivity is dominated by [2 + 2] cycloadditions.
For kctcnimincs, this reaction appears to be the first example of a [4 + 2] cycloaddition. Afier presenting some pertinent experimental observations semi- empirical (AMI) calculations on reactants, rcgioisomeric products and possible intermediates are discussed. As the simplest model, cycloadditions between acrolein and ketenimine arc used to locate transition states of the twelve possible peri-, site-, and rcgioisomeric products. Finally, the reliability of these calculations is discussed and some prospects for future work are given.

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