Photocaged Hydrocarbons, Aldehydes, Ketones, Enones, and Carboxylic Acids and Esters that Release by the Norrish II Cleavage Protocol and Beyond: Controlled Photoinduced Fragrance Release

Abstract

Five families of caged fragrance compounds that allow the storage and release of the following small volatile organic molecules are described: terpene hydrocarbons, aldehydes, ketones, Michael-type α,β-unsaturated enones, and carboxylic acids and esters. These caged molecules are released by photoexcitation via carbonyl-directed hydrogentransfer processes and subsequent CC bond cleavage (Norrish Type II) or by didenitrogenation of diazirines.

Photosensitivity Reactions Induced by Photochemical Degradation of Drugs

“…19,40 Role of functional groups of drug molecules in photo reactivity A high degree of photochemical reactivity is displayed by drugs that are readily excited by light; in general, this assumes a π-electron system and / or an oxidable heteroatom (S) or easy to split single bonds. 31 a. Carbonyl group behaves as an electrophilic radical in the π* excited state. Typical reactions are reduction via intermolecular hydrogen abstraction and fragmentation either via radical cleavage of the C-C bond between a carbonyl carbon atom and a carbon atom in a α position ("Norrish Type I" reaction) (figure 1a) or via intramolecular decomposition of the γ-position in a C-H bond which reacts with the carbonyl group, resulting in a hydroxyl group formation and the formation of two carbon atom radicals ("Norrish Type II" reaction) (figure 1b).…”

A Sunscreen‐Based Photocage for Carbonyl Groups

“…Their removal, which is generally performed in neutral media, without the addition of any reagent, makes them appealing alternatives to conventional methods employing basic, acidic, reductive, or oxidative conditions. A salient feature of the process is accurate spatial and temporal control of the photodeprotection, and this has been exploited in advantageous approaches for the release of chemicals such as acids, bases, oxidants, ions, drugs, pheromones, or fragrances . In this context, PPGs have found a wide range of applications in organic chemistry, biochemistry, biology, polymer science, lithography, toiletry, pest control, and so on …”

“…Among the available PPGs, relatively few have found utility for caging carbonyl functional groups . These PPGs are applicable not only in multi‐step organic synthesis, where carbonyl groups often require protection against nucleophilic, oxidative, or reductive agents, but also for biological purposes to release bioactive compounds.…”

Sulfonylation of Benzylic C−H Bonds through the Reaction of Aryl(o‐tolyl)methanones with Sulfonyl Hydrazides or Sulfonyl Chlorides

“…For decades, photochemistry has been utilized as a powerful tool for the functionalization of C−H bonds with good chemoselectivity and regioselectivity . Aldehydes and ketones are widely used as photosensors in photochemical reactions, owing to their ability to absorb photons under illumination in certain regions of the electromagnetic spectrum . Another straightforward method has involved employing those small molecules as photocatalysts, as well as reactants .…”