1: With bromo-1,3,2-benzodioxaborole in dichloromethane T=-78°C; demethoxymethylation; 2: With acetic acid in dichloromethane T=-78 - 20°C; Ring cleavage;

bromo-1,3,2-benzodioxaborole in dichloromethane T=-78 - 0°C; Cyclization; demethoxymethylation;

bromo-1,3,2-benzodioxaborole in dichloromethane T=-78 - 0°C; Cyclization; demethoxymethylation;