On the origin of cis/trans stereoselectivity in intramolecular Diels-Alder reactions of substituted pentadienyl acrylates

A comprehensive density functional study

Michael N. Paddon-Row*, Damian Moran, Garth A. Jones, Michael S. Sherburn

*Corresponding author for this work

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

A gas-phase B3LYP/6-31+G(d) study of substituent effects on the stereochemistry of both intramolecular Diels-Alder (IMDA) reactions of 9-E- and 9-Z-substituted pentadienyl acrylates and intermolecular Diels-Alder (DA) reactions between butadiene and monosubstituted alkenes and 3-substituted acrylates is reported and involves the calculation of 230 transition structures. It was found that, although exo ("anti-Alder") addition of monosubstituted ethenes to butadiene is the norm, Alder endo selectivity is more widely predicted for 3-substituted methyl acrylate dienophiles, and this was explained in terms of secondary orbital interactions (SOIs). Whereas cis/trans selectivity for IMDA reactions involving 9-5-substituted pentadienyl acrylates generally follows the normal pattern found for the corresponding intermolecular DA reactions, the 9-Z-substituted stereoisomers generally displayed trans selectivity that was much stronger than can be attributed to effects of the isolated substituent. This is strikingly so with unsaturated electron-withdrawing substituents whose endo selectivities, displayed in intermolecular DA reactions, are reversed in the IMDA reactions of pentadienyl acrylates. The origin of this anomalous Z-effect is explained in terms of the twist-mode asynchronicity concept of Brown and Houk. These ideas are used to explain the stereochemical outcomes of IMDA reactions of other triene systems.

Original languageEnglish
Pages (from-to)10841-10853
Number of pages13
JournalJournal of Organic Chemistry
Volume70
Issue number26
DOIs
Publication statusPublished - 23 Dec 2005
Externally publishedYes

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