Palladium(II)-catalyzed alkenyl C-H bond functionalization

Abstract

Firstly, we have developed an efficient methodology for the oxidative crosscoupling reaction of olefins with acrylates catalyzed by palladium under mild conditions to form the corresponding dienoates. In our method, both aromatic and aliphatic alkenes could afford the desired dienoate compounds in moderate to good yields. Besides terminal olefins, internal alkenes could also afford the corresponding products. This protocol offers several advantages including commercially available starting materials, operational simplicity, mild reaction conditions, high atom-economy, and moderate to high yields, which makes it potentially a useful and attractive strategy for the synthesis of dienoate compounds. Next, we have developed the first successful olefination reaction of enamides at the β-position with electron-poor alkenes catalyzed by Pd(OAc)2 and 1 atm oxygen as the sole oxidant. The corresponding products were obtained in moderate to high yields with excellent regioselectivity. The mechanism of this coupling reaction was also well studied by 1H NMR spectroscopic analysis, which showed that a vinylpalladium intermediate was involved in the coupling process. This novel method produces highly functionalized, versatile compounds which can be converted to a wide variety of building blocks and complex molecules. We have also developed an efficient cross-coupling of vinyl acetates with acrylates via Pd(OAc)2 catalyzed C-H activation of vinyl acetates to afford products in moderate to high yields with high regioselectivity. Moreover, this cross coupling reaction is a very novel method since no metal oxidant and/or additive is used. This elegant protocol allows for the formation of highly functionalized, versatile compounds which can be further manipulated to form a wide variety of synthetic intermediates and complex products.