INTRAMOLECULAR META PHOTOCYCLOADDITION OF CONFORMATIONALLY RESTRAINED5-PHENYLPENT-1-ENES .2. STERIC AND ELECTRONIC EFFECTS CAUSED BY 4-MONOSUBSTITUTION AND 4-DISUBSTITUTION

The meta photocycloaddition of 4-substituted 5-phenylpent-1-enes, 10 - 18, has been studied. The monosubstituted derivatives always prefer 2 ,6 addition, independent of the size of the substituent. For 2,6 addit ion two basic conformations are possible. Disubstituted compounds yiel d predominantly 1,3 addition with the sterically more demanding group exo. Except for the methoxymethyl and THF derivative the oxygen is fou nd exo as a result of repulsion, while the monohydroxy derivative give s also endo which might be explained by hydrogen bonding. The products from compound 11 change from mainly endo-OH in cyclohexane to chiefly exo-OH in methanol. Much similarity is found with Diels-Alder cycload dition.