Irradiation of a series of 5‐(2‐methoxyphenyl)pent‐1‐enes substituted with a hydroxy or trimethylsilyloxy group at the α‐, β‐, or γ‐position of the side‐chain yields in all cases meta photocycloadducts, in which the configuration at the substituted carbon atom is mainly endo. This indicates that the diastereoselectivity originates from minimization of steric interactions between the side‐chain substituent and the ortho‐methoxy group at the arene unit. Hydrogen bonding does not seem to be involved. The introduction of the side‐chain substituents also influences the regioselectivity of the addition: The linear to angular adduct ratios are significantly increased compared to the case of the parent compound.

1999 photochemistry, radiation chemistry, chemoluminescence photochemistry, radiation chemistry, chemoluminescence O 0160 -054Diastereoselective Intramolecular meta Photocycloaddition of Side-Chain-Substituted 5-(2-Methoxyphenyl)pent-1-enes.-Irradiation of the title pentenes (I) results in preferred formation of endo-configurated linear meta photoadducts. The selectivity is dictated by steric factors, hydrogen bonding does not seem to be important. -(TIMMERMANS, JOHAN L.; WAMELINK, MARC P.; LODDER, GERRIT; CORNELISSE, JAN; Eur. J.