Table 1.
Cyclodehydration of various 5‐keto‐aldonic acids and uronic acid derivatives in MeOH/HCl.[a]
| Entry | Substrate | Reaction time [h] | Crude Me‐FFA yield[b] [mol %] |
|---|---|---|---|
| 1 | 5‐keto‐d‐gluconic acid (K salt) | 72 | 43 |
| 2 | 5‐keto‐l‐galactonic acid (CaOH salt) | 72 | 50 |
| 3 | 5‐keto‐l‐galactonic acid (CaOH salt) | 24 | 65 |
| 4 | 5‐keto‐d‐mannonic acid (Ca/Na salt) | 24 | 17 |
| 5 | d‐galacturonic acid (monohydrate) | 24 | 0 |
| 6 | d‐galacturonic acid (Na salt) | 24 | <1 |
| 7 | d‐glucuronic acid | 24 | <1 |
[a] Conditions: substrate (1.0 g) in 3n MeOH/HCl (10 mL), 65 °C. [b] Isolated yield of the product after extraction without purification (purity≈90–100 % based on GC and NMR analyses).