Mechanistic studies of UV assisted [4 + 2] cycloadditions in synthetic efforts toward vibsanin E.
Quantum chemical DFT calculations at the B3LYP/6-31G(d) level have been used to study the stereochemical course of the photochemical cycloaddition of enone 9 with dienes. The observed products of this photochemically induced cycloaddition showed a stereoselectivity, which is opposite to what would be expected by FMO considerations. The quantum chemical calculations revealed that the unusual stereoselectivity of the reaction can be rationalized by assuming a stereospecific photochemical cis-trans isomerization of enone 9 to trans isomer 9a followed by a thermal Diels-Alder reaction of the diene onto the highly reactive trans enone. The photochemical reaction step involves the selective formation of a twisted triplet intermediate, which accounts for the selectivity of the reaction.
Nikolai
Joachim
J
Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260-3000, USA.
Loe
Øystein
Ø
Dominiak
Paulina M
PM
Gerlitz
Oksana O
OO
Autschbach
Jochen
J
Davies
Huw M L
HM
D000475:Alkenes / Q000737:chemistry*; D003500:Cyclization; D004224:Diterpenes / Q000138:chemical synthesis* / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D008958:Models, Molecular; D010777:Photochemistry; D011789:Quantum Theory; D013237:Stereoisomerism; D014466:Ultraviolet Rays
D000475:Alkenes; D004224:Diterpenes; D007659:Ketones; C506848:vibsanin E