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.

Recueil des Truuuiu Chimiqiies des ED Nijmegen, The Netherlands (Receiued September 12, 1994) Abstract.T h e synthesis of sulfines (thione oxides) (2, 10 and 17) derived from three chiral dithio esters (1, 8 and 16) bearing a hydrogen a t the a-carbon atom is described. T h e sulfine bearing an amido group at C-a (2), does not racemizc and proved to be stable over a long pcriod.When C-a in the sulfine (10) bears a n acetoxy group the optical activity remained unchanged for ii period of two months; after longer storage a rearrangement to a mixture of dithioperoxy ester 12 and S-methyl ester 11 took place. With an alkyl group at C-a, the sulfine 17 undergoes a fast racemization and rearranges slowly to a mixture of S-ethyl ester 14, dithioperoxy ester 18 and S-vinyl thiosulfinate 19.

1995 sulfoxides, sulfones, sulfenes and derivatives sulfoxides, sulfones, sulfenes and derivatives (acyclic compounds) P 0450 -102Synthesis of Chiral Sulfines by Oxidation of Dithio Esters.-The oxidation of chiral sulfines bearing different substituents at C-. alpha. is carried out and the chiral integrity of the stereogenic center is studied. The sulfine bearing an amido group, compound (II), is stabilized by intramolecular hydrogen bonding and does not racemize. When C-α in the sulfine bears an acetoxy group, a rearrangement to a mixture of S-methyl ester (VI) and dithioperoxy ester (VII) takes place but the optical activity remains unchanged. With an alkyl group at C-α the sulfines (IX) and (X) undergo a fast racemization and rearrange to a mixture of (XI), (XII) and (XIII). -(VAN DER LINDEN, J. B.; TIMMERMANS, J. L.; ZWANENBURG, B.; Recl. Trav. Chim. Pays-Bas 114 (1995) 3, 91-96; Dep. Org. Chem., Univ., NL-6525 ED Nijmegen, Neth.; EN)