Copper(II)/Silver(I)‐Catalyzed Sequential Alkynylation and Annulation of Aliphatic Amides with Alkynyl Carboxylic Acids: Efficient Synthesis of Pyrrolidones
A highly efficient protocol for the synthesis of pyrrolidones by the copper‐catalyzed alkynylation/annulation of aliphatic amides with alkynyl carboxylic acids is discussed in this paper. A broad range of easily accessible alkynyl carboxylic acids were introduced at the β‐methyl group of aliphatic amides with the assistance of an 8‐aminoquinolyl auxiliary group via decarboxylation to achieve the subsequent cyclic C N bond formation within one hour. High selectivity of β‐methyl groups over methylene groups was observed, and the extension of this catalytic system to the activation of methylene C H bonds failed. The substrates with two different groups at the α‐position of the aliphatic amides lead to the formation of diastereoisomers which is determined by 1H NMR spectroscopy. The initially produced products with Z‐configurations can be easily transformed to the corresponding products with E‐configurations by the treatment with dilute p‐toluenesulfonic acid after the reaction. This catalytic tandem decarboxylative cyclization provides a new opportunity for the direct functionalization of sp3 C H bonds.
