Intramolecular Diels−Alder Reactions of Ester-Linked 1,3,8-Nonatrienes

Abstract

[structures: see text] Penta-1,3-dienyl acrylates undergo kinetically controlled intramolecular Diels-Alder (IMDA) reactions and DFT calculations (B3LYP/6-31+G(d)) predict stereoselectivities that are in very good agreement with the experimental values. The nature of the diene C1 substituent has virtually no influence upon reactivity or trans/cis-stereoselectivity whereas terminal C9 dienophile substituents have a substantial effect on both the reactivity and stereoselectivity of these IMDA reactions. The TSs highlight contributions from strain in the developing tether-containing ring, and steric and electronic effects between tether and dienophile substituents, thus providing insight into the origins of IMDA reactivity and stereoselectivity.

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“…As in the case of 1 , the IMDA of acrylate 2 displays cis selectivity, but is weaker, with cis ‐ 2 TS lying only 2.6 kJ mol −1 below trans ‐ 2 TS . The CBS‐QB3 cis/trans ratio at 180 °C is in accord with the experimental ratio12 (Scheme ). Unlike trans ‐ 1 TS , there is no significant transannular strain between the C4 and C7 groups in trans ‐ 2 TS ; H4 is 2.57 and 3.41 Å from C7 and O10, respectively, with the former distance being slightly larger than the sum of the van der Waals radii of a hydrogen and a carbon atom (Scheme ).…”

“…Our results point to strategies for improving cis / trans selectivities in IMDAs that are only weakly selective. For example, experimentally, the IMDA of the 9‐ E ‐carbomethoxy acrylate 13 gives a cis/trans product ratio of 42:58 (110 °C, toluene),12 which is reproduced by our B3LYP calculations (41:59), with an overall trans selectivity of only 0.7 kJ mol −1 (Scheme ). Noting that the amide tether in 5 is predicted to be more trans selective than the ester tether in 2 , we predict greater trans selectivity in the IMDA of the 9‐ E ‐carbomethoxy acrylamide 14 , compared with that of the corresponding acrylate 13 .…”

Halogenation effects in intramolecular furan Diels–Alder reactions: broad scope synthetic and computational studies

“…The lower reactivity of the Z-dienophiles compared to the E-dienophiles is in contrast to Organic & Biomolecular Chemistry Paper that observed in some other IMDA reactions using acyclic dienes. 13 Indeed, reaction of the E-substrates 1l and 1q and also the 2-haloallyl systems 1i, 1j, 1n and 1o requires the halogen to be on the more hindered face of the [2.2.1]-bicyclic ring system. We next decided to examine frontier orbital effects using DFT (B3LYP/6-31G(d)) 14 calculations to attempt to explain these results.…”

On the Effect of Tether Composition on cis/trans Selectivity in Intramolecular Diels–Alder Reactions

“…This goal remains elusive, notwithstanding recent significant progress towards delineating the various factors controlling IMDA stereochemistry. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In this paper, we explore, using density functional theory, the origin of cis/trans selectivity in IMDAs of 1,3,8nonatrienes, 1-9, possessing tethers that are three atoms long (Scheme 1). Given the experimental fact that IMDAs generally give kinetically controlled product distributions, the key to understanding cis/trans selectivity in these reac-Abstract: Intramolecular Diels-Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6-31+G(d) and CBS-QB3 levels of theory for a series of 1,3,8nonatrienes, H 2 C=CH À CH=CH À CH 2 À X À Z À CH=CH 2 [ À X À Z À = À CH 2 À CH 2 À (1); À O À C(=O) À (2); À CH 2 À C(=O) À (3); À O À CH 2 À (4); À NH À C(=O) À (5); ÀSÀC(=O)À (6); ÀOÀC(=S)À (7); ÀNHÀC(=S)À (8); ÀSÀC(=S)À (9)].…”