A base‐mediated carbocyclization study has been performed between two allowed Baldwin cyclization modes (6‐exo‐trig and 6‐exo‐dig) and it was found that 6‐exo‐trig cyclization was preferred over 6‐exo‐dig. Allyl cyanide was found to be suitable and efficient pronucleophile for this investigation and two sp2–sp2 transition‐metal‐free C−C bond formations took place in a single operation to yield two differently functionalized biaryl compounds.
A simple, efficient and economical synthesis of dimethyl 3-amino-5-(2-oxo-2-arylethyl)thiophene-2,4-dicarboxylates has been reported by ring opening of methyl 3-amino-6-aryl-4-oxo-4H-thieno[3,2-c]pyran-2-carboxylates by alkoxide ions.
A facile synthesis of highly functionalized spirobutenolides was carried out by a nitroalkane carbanion-induced ring opening and relactonization via a denitration reaction of 2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles and 2oxo-2,5-dihydrothiochromeno[4,3-b]pyran-3-carbonitriles. However, when nitroethane was used as a nucleophile source in lieu of nitromethane, a mixture of (E)-and (Z)-isomers of the corresponding spirobutenolides was obtained in a different ratio. The structure and geometry of the product were confirmed by single-crystal X-ray diffraction. The isolated (E)-and (Z)-butenolides with the treatment with sodium ethoxide in DMF at room temperature provided highly substituted trienes via an allylic ring opening followed by decarboxylation.
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