α-Functionally Substituted α,β-Unsaturated Aldehydes as Fine Chemicals Reagents: Synthesis and Application

Metal-Free Selective Synthesis of α,β-Unsaturated Aldehydes from Alkenes and Formaldehyde Catalyzed by Dimethylamine

α,β-Unsaturated aldehydes are important building blocks for the synthesis of a wide range of chemicals, including polymers. The synthesis of these molecules from cheap feedstocks such as alkenes remains a scientific challenge, mainly due to the low reactivity of alkenes. Here we report a selective and metal-free access to α,β-unsaturated aldehydes from alkenes with formaldehyde. This reaction is catalyzed by dimethylamine and affords α,β-unsaturated aldehydes in yields of up to 80 %. By combining Density Functional Theory (DFT) calculations and experiments, we elucidate the reaction mechanism which is based on a cascade of hydride transfer, hydrolysis and aldolization reactions. The reaction can be performed under very mild conditions (30-50 °C), in a theoretically 100 % carbon-economical fashion, with water as the only by-product. The reaction was successfully applied to non-activated linear 1-alkenes, thus opening an access to industrially relevant α,β-unsaturated aldehydes from cheap and widely abundant chemicals at large scale.

A facile synthesis of α,β-unsaturated imines via palladium-catalyzed dehydrogenation

The dehydrogenation adjacent to an electron-withdrawing group provides an efficient access to α,β-unsaturated compounds that serving as versatile synthons in organic chemistry. However, the α,β-desaturation of aliphatic imines has hitherto proven to be challenging due to easy hydrolysis and preferential dimerization. Herein, by employing a pre-fluorination and palladium-catalyzed dehydrogenation reaction sequence, the abundant simple aliphatic amides are amendable to the rapid construction of complex molecular architectures to produce α,β-unsaturated imines. Mechanistic investigations reveal a Pd(0)/Pd(II) catalytic cycle involving oxidative H-F elimination of N-fluoroamide followed by a smooth α,β-desaturation of the in-situ generated aliphatic imine intermediate. This protocol exhibits excellent functional group tolerance, and even the carbonyl groups are compatible without any competing dehydrogenation, allowing for late-stage functionalization of complex bioactive molecules. The synthetic utility of this transformation has been further demonstrated by a diversity-oriented derivatization and a concise formal synthesis of (±)-alloyohimbane.

Electrophilic Fluorination of Silyl Dienol Ethers: a General and Selective Access to γ-Fluoro Enals

We describe the direct synthesis of γ-fluoro enals from the corresponding silyl dienol ethers. This simple process operates under mild conditions and is compatible with a wide range of functionalities. The high γ regioselectivity of this protocol was rationalized by means of theoretical calculations.

Barbier polymerization induced emission of cinnamaldehyde: a one-pot Grignard reaction?

The Grignard reaction of cinnamaldehyde is demonstrated to give a 1,2-addition product, while the Barbier reaction of cinnamaldehyde yields a macromolecule with aggregation-induced emission type non-conjugated luminescence properties.