Estudo da reação de hidroformilação de derivados de (-)- isopulegol e (+)-neoisopulegol catalisada por complexo de ródio (i)

Abstract

-)-isopulegol and (+)-neoisopulegol are examples of monoterpenes whose reactions of functionalization of carbon-carbon Double bond can be influenced by the presence of two stereogenic centers. The study of the reaction of hydroformylation of monoterpenes derived from protected with acetyl groups, benzyl, benzoyl, MOM and TBDMS consists in addition of (CO and H2) synthesis gas the group propilideno generating aldehydes that are useful for the synthesis of new intermediates an also represent compounds of great importance to the cosmetics industry, perfumery and pharmaceuticals. The reaction was performed under mild conditions (80°C and 80 bar CO/H2) and in the presence of catalytic precursor acac Rh(CO)2(C5H7O2), modified or no by ligands, obtaining in all cases only the isomer coresponding linear aldehyde. The optimization of reaction conditions (temperature and pressure CO/H2) the use of different phosphorus ligands and the way in which the protecting groups influence the reaction, are crucial for understanding the selectivity of products. The efficiency in the hydroformylation of these derivatives is attributed to special properties of the ligand P(O-otBuPh)3, which has a large cone angle θ=175° which disfavors the coordination of another ligand in the coordination sphere. Even at high ratios P/Rh, the catalytically active species have only one phosphite connected, thus enabling that olefin occupies the remaining space and coordinate to the metal. Another factor is the insertion of CO on Rh-alkyl bond is favored due to the fact that this ligand is a weak σ-eletrodoador and a strong π-eletrorretirador. The protecting groups play na important role, as well as preventing the cyclization influence the selectivity of products through eletronic and steric effects. The reaction catalyzed by rhodium using PPh3 as ligand proved to be ineffective because there was no conversion of the substrate in any of the tests. Among the substrates studied, the (-)-isopulegol protected wih TBDMS presented the best selectivity since it resulted in 100% conversion resulting in only a linear aldehyde. All tests for derivatives of (+)- neoisopulegol showed the same selectivity (1:1) for products.