Obtenção de novas fragrâncias via oxidação aeróbica de olefinas catalisada por sais de paládio

Abstract

The catalytic oxidation represents a crucial tool for the synthesis of compounds potentially applicable as fragrances and pharmaceuticals. The oxidation of several olefins with different structural complexities was studied in homogeneous systems using palladium catalysts and molecular oxygen as the final oxidant. Cis-jasmone, the main constituent of the jasmine essential oil, has two internal olefinic bonds that can interact with the metal center. Depending on the catalytic system and solvent employed, the formation of either allyl oxidation products or ketones can be performed. In acetic acid solutions and with stoichiometric amounts of p-benzoquinone, it was possible to obtain the allyl acetate derived from the functionalization of the acyclic double bond of the substrate with selectivity of up to 80%. Efficient catalytic turnovers with respect to p-benzoquinone could be achieved either under atmospheric pressure using catalytic amounts of Cu(OAc)₂ as an electron transfer mediator to promote the regeneration of p-benzoquinone, or under the oxygen pressure of 5 and 10 atm in the absence of any auxiliary cocatalyst. Alternatively, cis-jasmone can be oxidized to ketones in aqueous solutions of dimethylacetamide using molecular oxygen as the final oxidant and PdCl₂ as the sole catalyst. The poly-functionalized oxygenated jasmonoides obtained in these reactions from the bio-renewable substrate are potentially useful as components of perfumes and cosmetic products. Palladium catalyzed oxidation of olefins with molecular oxygen is a synthetically important reaction and the solvent plays a critical role in the process. Combining the success of these catalytic processes with the current concern for the environment, it has been studied the oxidation of a series of olefins in solvents less harmful to the environment aiming to replace problematic solvents conventionally used in these reactions. Several green solvents were tested as a reaction medium for the allylic oxidation of a series of alkenes. Dimethylcarbonate, methyl isobutyl ketone, and propylene carbonate, solvents with impressive sustainability ranks and very scarcely exploited in palladium catalyzed oxidations, were proved to be excellent alternatives for the solvents conventionally employed in these processes, such as acetic acid. Palladium acetate alone or in the combination with p-benzoquinone efficiently operates as the catalyst for the oxidation of alkenes by dioxygen under 5–10 atm. The methodology developed allowed to produce valuable oxyfunctionalized products from various olefins through an environmentally more friendly process. These products are potentially useful as synthetic intermediates or in the preparation of formulations for the pharmaceutical or perfume industry.