tert-butyl 5'-bromo-3'H-spiro[azetidine-3,1'-[2]benzofuran]-1-carboxylate; tert-Butyl 5'-bromo-3'H-spiro[azetidine-3,1'-isobenzofuran]-1-carboxylate; 5'-Bromo-spiro[azetidine-3,1'(3'H)-isobenzofuran]-1-carboxylic acid, 1,1-dimethylethyl ester;