Herein, we describe a Pd-catalyzed
[2+3] cycloaddition/cross-coupling
reaction of allenyl acetates for the Z/E selective
and diastereoselective synthesis of dendralene-functionalized dihydrofurans.
Remarkably, mechanistic studies show the formation of an epoxide from
a carbonyl bond via cycloaddition, which is practically and mechanistically
significant for the construction of other bioactive heterocyclic epoxides.
This research also revealed the utility and potential of allenic esters
as C2 synthons and 1,2-biselectrophiles in cycloaddition reactions.
Herein, we report an elemental sulfur-promoted switchable redox condensation reaction that can selectively prepare 2-aminofurans and 2-aminothiophenes from the corresponding enaminones and methylene nitriles, respectively. Mechanistic studies demonstrated that the enaminones, as dual nucleophiles, reacted with nitrile acetate to produce 2-aminofurans via 3,5annulation under promotion by elemental sulfur. These reactions used readily available starting materials, transition metal-free, ecofriendly procedures, gram-scale syntheses, and wide functional group tolerance. The methodology may be useful for the construction of 2-aminofuran and 2-aminothiophene derivatives with potential biological activity.
Herein, we report a green cascade approach to prepare
a variety
of diastereoselective polysubstituted cyclopentene derivatives through
metal-free oxidative [2 + 1 + 1 + 1] annulation of aldehydes and methylene
nitriles. Mechanistic studies demonstrated that the reaction underwent
a four-step cascade reaction including air oxidation and Michael addition
to obtain the final product. This reaction features readily available
starting materials, transition metal-free, eco-friendly operations,
gram-scale syntheses, and wide functional group tolerance. The methodology
may be useful for the construction of polysubstituted cyano-cyclopentene
heterocycles with potential biological activity.
Lawsones and indenopyrazoles are the prevalent structural motifs and building blocks in pharmaceuticals and bioactive molecules, but their synthesis has always remained challenging as no comprehensive protocol has been outlined to date. Herein, a metal-free, ring-expansion reaction of indantrione with diazomethanes, generated in situ from the N-tosylhydrazones, has been developed for the synthesis of lawsone and indenopyrazole derivatives in acetonitrile and alcohol solvents, respectively. It provides these valuable lawsone and pyrazole skeletons in good yields and high levels of diastereoselectivity from simple and readily available starting materials. DFT calculations were used to explore the mechanism in different solutions. The synthetic application example also showed the prospects of this method for the preparation of valuable compounds.
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