Spin-directed stereoselectivity of carbonyl-alkene photocycloadditions
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.
Griesbeck
AG
Institute of Organic Chemistry, Greinstrasse 4, and Institute of Physical Chemistry, Luxemburger Strasse 116, University of Cologne, D-50939 Koln, Germany.
Fiege
M
Bondock
S
Gudipati
MS