title: Ene reaction of singlet oxygen, triazolinedione, and nitrosoarene with chiral deuterium-labeled allylic alcohols: the interdependence of diastereoselectivity and regioselectivity discloses mechanistic insights into the hydroxy-group directivity.
abstract: The ene reaction of singlet oxygen ((1)O(2)), triazolinedione (TAD), and nitrosoarene, specifically 4-nitronitrosobenzene (ArNO), with the tetrasubstituted 1,3-allylically strained, chiral allylic alcohol 3,4-dimethylpent-3-en-2-ol (2) leads to the threo-configured ene products in high diastereoselectivity, a consequence of the hydroxy-group directivity. Hydrogen bonding favors formation of the threo-configured encounter complex threo-EC in the early stage of ene reaction. For the analogous twix deuterium-labeled allylic alcohol Z-2-d(3), a hitherto unrecognized dichotomy between (1)O(2) and the ArNO and TAD enophiles is disclosed in the regioselectivity of the tetrasubstituted alcohol: Whereas for ArNO and TAD, hydrogen bonding with the allylic hydroxy group dictates the regioselectivity (twix selectivity), for (1)O(2), the cis effect dominates (twin/trix selectivity). From the interdependence between the twix/twin regioselectivity and the threo/erythro diastereoselectivity, it has been recognized that the enophile also attacks the allylic alcohol from the erythro pi face without assistance by hydrogen bonding with the allylic hydroxy functionality.
authors.affiliation: Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany. adam@chemie.uni-wuerzburg.de
authors.forename: Waldemar
authors.initials: W
authors.lastname: Adam
authors.forename: Nils
authors.initials: N
authors.lastname: Bottke
authors.forename: Oliver
authors.initials: O
authors.lastname: Krebs
authors.forename: Ioannis
authors.initials: I
authors.lastname: Lykakis
authors.forename: Michael
authors.initials: M
authors.lastname: Orfanopoulos
authors.forename: Manolis
authors.initials: M
authors.lastname: Stratakis