Efficient synthesis of 2H-chromene derivatives via a dual-organocatalytic reaction

Copper(II)-catalyzed direct dehydrative alkynylation of 2H-chromene hemiketals with terminal alkynes to 2,2-disubstituted 2-alkynylated 2H-chromenes

The first copper-catalyzed direct dehydrative alkynylation of 2H-chromene hemiketals with terminal alkynes has been uncovered. The use of cheap and readily available CuCl₂ as the catalyst allowed the preparation of various 2,2-disubstituted 2-alkynylated 2H-chromenes in moderate to good yields, which compensates for the limitation of the current methods only suited for the synthesis of 2-monosubsituted 2-alkynylated 2H-chromenes.

Efficient Synthesis of 3-Sulfonyl-2-sulfonylmethyl-2H-chromenes via Tandem Knoevenagel Condensation/Oxa-Michael Addition Protocol

An organocatalytic [4 + 2] cascade annulation of salicylaldehydes and 1,3-bisarylsulfonylpropenes has been developed. This protocol enables the efficient and straightforward synthesis of a new series of 3-sulfonyl-2-sulfonylmethyl-2H-chromenes that are useful for exploring pharmacologically valued compounds. Further reductive modifications result in 3-desulfonylated chromene or chromane derivatives. This protocol can be expanded to the synthesis of 3-sulfonyl-2-sulfonylmethyl 1,2-dihydroquinoline.

Direct Synthesis of Coumarin Derivatives from Alkynoic Esters via Dual-organocatalysis

An efficient synthetic method for coumarin derivatives was developed using a dual-organocatalytic reaction. A combination of p-toluenesulfonic acid monohydrate and piperidine was found to efficiently catalyze the cyclization between salicylaldehydes and alkynoic esters to give various coumarin derivatives in good yield and high selectivity. Mechanistic and kinetic data suggested that the conjugate addition between piperidine and alkynoic esters played a crucial role in the reaction mechanism.

Synthesis of 2H-chromenes: recent advances and perspectives

As one type of chromene, 2H-chromenes represent important oxygen heterocycles, which not only widely exist in natural products, pharmaceutical agents and biologically relevant molecules, but have also been used broadly in materials science and organic synthesis. Two major synthetic strategies have been developed towards such compounds. This review mainly focuses on the recent advances in this field, including benzopyran ring formation involving cyclization reactions and the late-stage functionalization of the parent 2H-chromenes.