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Article

On the Origin of Cis/Trans Stereoselectivity in Intramolecular Diels−Alder Reactions of Substituted Pentadienyl Acrylates: A Comprehensive Density Functional Study

Supporting Info

Michael N. Paddon-Row,*^† Damian Moran,^† Garth A. Jones,^† and Michael S. Sherburn^‡

School of Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia, and Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia

J. Org. Chem., 2005, 70 (26), pp 10841–10853

DOI: 10.1021/jo051973q

Publication Date (Web): November 8, 2005

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

†

University of New South Wales.

‡

Australian National University.

, m.paddonrow@unsw.edu.au

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-E-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.