General procedure for the synthesis of 5,6-O-isopropylidene-L-ascorbic acid from vitamin C: Vitamin C (1.76 g, 10 mmol) and acetone (9 mL) were added to a reaction flask fitted with a magnetic stirrer and stirred until dissolved. Subsequently, phosphoryl chloride (0.5 mL) was added slowly and dropwise to the above solution. The reaction mixture was stirred continuously for 4 hours at room temperature. After completion of the reaction, the mixture was filtered, and the filter cake was washed with cold acetone-water (volume ratio adjusted according to the actual situation), and finally dried under vacuum to obtain the target compound 5,6-O-isopropylidene-L-ascorbic acid (1.92 g, 89% yield) as a colorless granular solid. The product was detected by IR (KBr press method) and the main absorption peaks were: νmax 3242.6, 2993.3, 2907.6, 2741.6, 1755.5, 1665.4 cm-1. 1H NMR (600 MHz, CD3COCD3) data: δ 4.71-4.73 (m, 1H, C4-H), 4.37-4.39 ( m, 1H, C5-H), 4.16-4.21 (m, 1H, C6-H), 3.99-4.03 (m, 1H, C6-H), 1.29 (s, 6H, Me).
