This contribution describes a regioselective cyclization of hypervalent iodine reagents (HIR) with propiolic acids in the presence of a rhodium catalyst. The mild decarboxylation can tolerate a wide range of groups and generates 4H‐furo[3,2‐c]chromen‐4‐one derivatives in good isolated yields.magnified image
A new Ag2O‐promoted cascade reaction of 4‐hydroxycoumarins with α‐keto acids under mircowave irradiation has been developed. The reaction provides an efficient approach to fused chromenes with quaternary stereocenters in 10 min, and gives good yields. Chromene derivatives can be prepared on a gram scale using this method.
An efficient silver-catalyzed stereoselective transaddition of 4-hydroxycoumarins to haloalkynes under ambient air is described, allowing the straightforward synthesis of vinyl halides. The late-stage nitration of the resulting products with silver nitrate proceeded with retention of configuration, affording a series of nitroalkenes in good yields. Additionally, DFT calculations were employed for mechanistic studies, and a possible mechanism for the Ag(I)catalyzed addition was proposed.
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