title: Spin-directed stereoselectivity of carbonyl-alkene photocycloadditions
abstract: The concentration dependence of the Paterno-Buchi photocycloaddition of the two cyclic enolethers 2,3-dihydrofuran and 2,3-dihydropyran, respectively, with aromatic as well as aliphatic aldehydes was studied. For aliphatic aldehydes, a sharp transition from low to high diastereostereoselectivity was observed, indicating a switch from singlet to triplet photocycloaddition with different selectivity controlling mechanisms.
authors.affiliation: Institute of Organic Chemistry, Greinstrasse 4, and Institute of Physical Chemistry, Luxemburger Strasse 116, University of Cologne, D-50939 Koln, Germany.
authors.initials: AG
authors.lastname: Griesbeck
authors.initials: M
authors.lastname: Fiege
authors.initials: S
authors.lastname: Bondock
authors.initials: MS
authors.lastname: Gudipati