Alkyl or aryl a-keto esters of primary or secondary alcohols decompose upon irradiation at 350 ± 370 nm from the intermediate triplet state into aldehydes or ketones in polar, as well as apolar solvents. The use of these keto esters as delivery systems for the controlled release of perfumery aldehydes and ketones was investigated by photoirradiation in the presence of oxygen with a Xe or UV lamp, as well as outdoor sunlight. Systematic GC/ MS analysis of the irradiated solutions showed that, under these conditions, the desired Norrish type-II fragmentation of the ester side chain is the predominant reaction pathway in most of the cases. g-H Abstraction from the alkyl side chain of alkyl keto esters, as well as an intramolecular PaternoÁ-Büchi reaction or epoxidation of the alkene function in different citronellyl a-keto esters were identified as the most important side reactions. Some of the experimental findings have been rationalized on the basis of ab initio and density-functional calculations. (Cyclohexyl)oxoacetates and oxo(phenyl)acetates were found to be the most suitable precursors for the desired perfumery applications.1. Introduction. ± Aldehydes and ketones are important classes of fragrances that are present in all kinds of perfumes. However, many of them are very volatile and can, after application, only be perceived over a relatively short period of time. Furthermore, as constituents of perfumes for a variety of different bodycare or household applications, such as shampoos, soaps, all purpose cleaners, fabric softeners, or detergent powders, they are often too hydrophilic and thus easily carried away by water during various rinsing processes instead of staying on substrates like hair, skin, or fabrics.To prolong the desired odor perception of this class of compounds, we have prepared a series of photolabile, hydrophobic, non-volatile fragrance precursors as potential delivery systems for the controlled release of perfumery aldehydes and ketones in typical bodycare and household applications. In this publication, we describe the fragrance release from a-keto esters upon irradiation with artificial light sources, as well as natural sunlight in the presence of O 2 [1]. Some interesting fragrances for release in functional perfumery are depicted in Fig. 1 [2].The photolysis of alkyl or aryl a-keto esters of primary or secondary alcohols has been intensively studied since the early sixties [3 ± 7]. It was found that these esters decompose from their intermediate triplet state into aldehydes or ketones upon irradiation at 350 ± 370 nm in polar, as well as apolar solvents [7 ± 11]. Most of the photoirradiations described in the literature were carried out in degassed solutions in the absence of O 2 . The relatively good yields of the fragmentation process have allowed the use of a-keto esters as intermediates for the transformation of primary or secondary alcohols to aldehydes and ketones, respectively [12].