Aerobic oxidative esterification reaction

Cinnamils (162) have surprisingly been found to evolve towards 2,3,8-triaryl vinyl fulvenes (163) and o-terphenyl derivatives (164) under NHC catalysis. The formation of these products has been rationalized via a mechanism involving a complex cascade process. Finally, a mechanistic investigation has been carried out on the NHC-catalysed aerobic oxidative esterification of aromatic aldehydes.Aryloin species have not only been identified as key intermediates of such oxidative reactions, but most importantly is that they have been shown to be the species which react with oxygen in the air and not the Breslow intermediates as previously suggested. 

Palladium catalysts are widely used in liquid phase aerobic oxidations, and numerous examples have been employed for large-scale chemical production (Scheme 8.1). Several industrially important examples are the focus ofdedicated chapters in this book Wacker and Wacker-type oxidation of alkenes into aldehydes, ketones, and acetals (Scheme 8.1a Chapters 9 and 11), 1,4-diacetoxylation of 1,3-butadiene (Scheme 8.1b Chapter 10), and oxidative esterification of methacrolein to methyl methacrylate (Scheme 8.1c Chapter 13). In this introductory chapter, we survey a number of other Pd-catalyzed oxidation reactions that have industrial significance, including acetoxylation of ethylene to vinyl acetate (Scheme 8. Id), oxidative carbonylation of alcohols to dialkyl oxalates and carbonates (Scheme 8.1e), and oxidative coupling of dimethyl phthalate to 3,3, 4,4 -tetramethyl biphenylcarboxy-late (Scheme 8.1f). 

Isotopic-labeling experiments and evidence of a dimeric intermediate in the transition-metal-free aerobic oxidative C-C bond cleavage of a-hydroxy ketones and their esterification, on reaction with O2 as the ideal oxidant in the presence of K2CO3, have disclosed the reaction mechanism. ... 

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