ABSTRACT
A TBAB-mediated brominative 5-exo-dig oxy-cyclization of 2-alkynylbenzamide is described here for the synthesis of isobenzofuran-1-imines and isobenzofuran derivatives at room temperature with a high efficiency and a broad reaction scope. The resulting isobenzofuran derivatives are also applied for synthesising various substituted isobenzofuran derivatives.
ABSTRACT
A regioselective 2,4-dibromohydration of conjugated enynes is reported for the synthesis of 2-(2,4-dibromobut-2-enoyl)benzoate. In the presence of tetra-n-butylammonium bromide and H2O the transformation proceeds smoothly with good reaction efficiency and a broad reaction scope. Mechanism studies indicate that the neighboring ester group participates in the 2,4-dibromohydration, and the oxygen atom of ester is transferred into the C-C triple bond to form the keto carbonyl group in the product. 2-(2,4-Dibromobut-2-enoyl)benzoate is recognized as an important synthon toward phthalazin-1(2H)-one and the natural product Shihunine.
ABSTRACT
Bromide mediated neighboring ester-participating bromocyclizations of o-alkynylbenzoates are described here for the synthesis of benzil-o-carboxylates. 4-bromoisocoumarins are also synthesized when phenyl o-alkynylbenzoate is used as the substrate. Mechanistic studies suggest that the whole process is composed of an electrophilic bromocyclization and a dibromohydration-based ring-opening, and the neighboring ester group participates in the bromocyclization. Interestingly, the two oxygen atoms of the keto carbonyls in benzil-o-carboxylates are both derived from water. The electrophilic bromo source is in situ generated from the oxidation of bromide.