Substituent Effect on exo Stereoselectivity in the 1,3-Dipolar Cycloaddition Reaction of Tulipalin A with Nitrile Ylides
| Autoři | |
|---|---|
| Rok publikování | 2008 |
| Druh | Článek v odborném periodiku |
| Časopis / Zdroj | Journal of Organic Chemistry |
| Fakulta / Pracoviště MU | |
| Citace | |
| Obor | Organická chemie |
| Klíčová slova | CH-pi Interaction; Substituent effect; stereoselectivity; cycloaddition |
| Popis | 1,3-Dipolar cycloaddition reactions of dihydro-3-methylene-2(3H)-furanone (Tulipalin A) with various benzonitrile(p-X-benzylide) ylides prefer formation of exo-cycloadducts in the extent of corresponding to an increasing electron donor character of the substituent X in p-position of benzylide phenyl ring of 1,3-dipolar reagent. The substituent effect on diastereoselectivity of the 1,3-DC reaction is rationalized in terms of CH/p interaction between dipole and dipolarophile in an exo-transition state. The interaction is demonstrated by the correlation of the observed diastereoselectivities with substituent Hammett sigma constants, which shows a small negative r value. A certain contribution of CO/p interaction between lactone carbonyl and the substituted phenyl ring to mediation of the substituent effect is also discussed. The energy profiles of both reaction pathways were analyzed using DFT and RI-MP2 theoretical approaches. Calculated energy and structural differences between located transition states are consistent with reaction diastereoselectivities. |