Reactions using micellar systems. IV. Regioselectivity in the photodimerizations of 2-pyridones in micelles and reversed micelles.

Abstract

Photodimerizations of N-alkyl-2-pyridones (1a-e), N-ω-carboxyalkyl-2-pyridones (1f-h), and N-2'-carboxyethyl-4-alkyl-2-pyridones (1i and 1j) in micellar and reversed micellar systems gave the following results ; 1) in the reactions of 1a-e, the cis/trans ratios of dimers increased with decreasing concentration of the probes, with the octyl compound (1d) showing the highest selectivity ; 2) in the case of 1f-h, the ratios increased up to 1.0 with decreasing alkyl chain length ; 3) below 7.2 mM concentration, 1i gave exclusively the cis dimer, while only the trans dimer was formed when the reaction was carried out in water. The results indicate that the regio-control of the reactions was a result of the alignment effect of micelles on the substrate, and moreover, in both micellar systems, not only the distribution of amphiphilic probes between micellar and bulk (water or cyclohexane) phases but also the orientation and incorporation site of the pyridone moiety play important roles in the regioselectively for the cis dimer.