Versatile stereoselective oxidative alkoxycarbonylation of styrenes at room-temperature

Carbonylation reactions carried out at room temperature and at atmospheric pressure of carbon monoxide are highly attractive and extremely rare at the same time. Here, the oxidative alkoxycarbonylation of styrenes to industrially relevant cinnamates has been developed under such a mild conditions (rt, 1 atm of CO) in the presence of a palladium(II) complex bearing a bis(aryl)acenaphthenequinonediimine ligand, benzoquinone and p-toluenesulfonic acid. Remarkably, variously substituted styrene derivatives have been efficiently carbonylated using a nearly stoichiometric amount of alcohols, with a dramatic reduction of waste. Even reluctant internal alkenes have shown to be compatible under these carbonylative conditions. In consideration of experimental results and DFT calculations a mechanistic rationale has been proposed. Based on this study, the benzoquinone has been found to promote the final palladium reoxidation, and to boost the reaction under such unprecedent mild conditions. The present methodology has been successfully exploited for the synthesis of high value-added cinnamoyl glycerols and cinnamic acid sugar esters, including the 6-O-p-coumaroyl-D-glucose natural product.