No abstract

A mild, metal‐free synthesis of polyfunctionalized N‐acyl‐N,O‐hemiacetals was developed via the nucleophilic addition of unactivated amides to ketones. The protocol demonstrated a wide substrate scope, with good isolated yields. Additionally, their O‐acetylated products serve as a precursor of α,α‐difunctionalized N‐acylimines. An addition reaction of broad scope of nucleophiles to generate N‐acylimines is also reported.magnified image

A methylene group inserted between proximal carbonyl groups underwent exclusive oxyfunctionalization with sodium chlorite in the presence of redox‐inert HfIV in water. Direct oxidation methods have conventionally suffered from manifold side reactions such as oxidative fragmentation, dimerization, and overreactions, together with the use of toxic and intractable oxidants. Although alternative routes involving prior α‐functionalization can be executed under mild conditions, preparatively valuable oxidation methods that deliver high levels of both conversion and selectivity remain a prized goal from the standpoint of streamlining organic synthesis. Chlorine dioxide, which was generated as a yellowish gas during the reaction, is considered to be a bona fide oxidant against active methylene compounds. The pivotal role of water was clear, given that the reaction was significantly retarded in both aqueous acetonitrile and ethanol, which can solubilize sodium chlorite.

Various tetra-acceptor-substituted alkenes possessing unsymmetrical substituents have been effectively synthesized from vicinal tricarbonyl compounds. The alkenes have polyfunctionality and high electron deficiency. In addition, they easily react with pyrroles to give divergent pyrrolizine derivatives via the conjugate addition of pyrroles followed by intramolecular cyclization. We successfully controlled the chemoselectivity of the intramolecular cyclization (ester/ketone attack) to afford a wide range of valuable pyrrolizine derivatives.

Diethyl mesoxalate (DEMO) exhibits high electrophilicity and accepts the nucleophilic addition of a less nucleophilic acid amide to afford N,O-hemiacetal. However, our research showed that elimination of the amide moiety...