%0 Generic %A Bach, Thorsten %A Grosch, Benjamin %A Strassner, Thomas %A Herdtweck, Eberhardt %D 2003 %T Enantioselective [6π]-Photocyclization Reaction of an Acrylanilide Mediated by a Chiral Host. Interplay between Enantioselective Ring Closure and Enantioselective Protonation %U https://acs.figshare.com/articles/dataset/Enantioselective_6_-Photocyclization_Reaction_of_an_Acrylanilide_Mediated_by_a_Chiral_Host_Interplay_between_Enantioselective_Ring_Closure_and_Enantioselective_Protonation/3697149 %R 10.1021/jo026602d.s004 %2 https://acs.figshare.com/ndownloader/files/5787579 %K trans product ent %K intermediates 8 %K chiral lactam 4 %K Enantioselective Ring Closure %K trans compound ent %K cis compound ent %K amide 4 favor %K chiral amide 4 %K DFT %K enantioselective protonation %K NMR %K enantioselective ring closure %K chiral complexing agent %K conrotatory ring closure %X The [6π]-photocyclization of the anilides 1a and 5 was studied in the absence and in the presence of the enantiomerically pure chiral lactam 4. The relative configuration of the products was unambiguously established by single-crystal X-ray crystallography and by NMR spectroscopy. A significant enantiomeric excess was observed upon reaction of compound 1a to its photocyclization products at −55 °C employing lactam 4 as a chiral complexing agent in toluene as the solvent (66% yield). The trans product ent-3a was obtained in 57% ee, and the minor diastereoisomer (trans/cis = 73/27), cis product ent-2a, was obtained in 30% ee. DFT calculations were conducted modeling the complexation of intermediates 8 and ent-8 to host 4. In agreement with steric arguments concerning the conrotatory ring closure of 1a, the formation of ent-8 is favored leading to the more stable complex 4·ent-8 as compared to 4·8. Whereas the enantioselectivity in the photocyclization to trans compound ent-3a increased upon reduction in the reaction temperature, the enantiomeric excess in the formation of cis compound ent-2a went through a maximum at −15 °C (45% ee) and decreased at lower temperatures. Deuteration experiments conducted with the pentadeuterated analogue of 1a, d5-1a, revealed that the protonation of the intermediates 8 and ent-8 is influenced by chiral amide 4. In the formation of ent-3a/3a, both the enantioselective ring closure and the enantioselective protonation by amide 4 favor the observed (6aS,10aS)-configuration of the major enantiomer ent-3a. In the formation of ent-2a/2a, the enantioselective ring closure (and the subsequent diastereoselective protonation) favors the (6aR,10aS)-configuration that is found in compound 2a. Contrary to that, the enantioselective protonation by amide 4 shows a preference for ent-2a with the (6aS,10aR)-configuration. %I ACS Publications