Metal free synthesis of 2,3-dideoxy-α, β-unsaturated carbohydrate enals (Perlin aldehydes)

• Published in: Carbohydrate research 2023-09, Vol.531, p.108890-108890, Article 108890
• Main Authors: Singh, Kavita, Behera, Sourav Sagar, Tyagi, Rajdeep, Tiwari, Ghanshyam, Sagar, Ram
• Format: Article
• Language: English
• Subjects: Aldehydes; Carbohydrates; Metals; Water
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/j.carres.2023.108890

A metal free synthesis of enantiopure 2,3-dideoxy-α, β-unsaturated carbohydrate enals (Perlin aldehydes), in CH3CN-0.02 N H2SO4 in water (1:1, v/v) with 0.5 equivalent additives (4-hydroxy-6-methyl-2-pyrone or 4-amino coumarin), has been reported. This efficient protocol works well for the acetylated glycals (glucal, galactal and arabinal) and afforded Perlin aldehydes and hemiacetals in acceptable to good yields. Whereas, benzylated glycals furnished respective Perlin aldehydes, hemiacetals and the 2-deoxy derivatives, under similar reaction conditions. The products yields were significantly reduced when the additives were removed from the reaction mixture, indicating that they constitute an essential component of this approach. Further the use of 0.02 N H2SO4 in water: acetonitrile (1:1, v/v) solvent system is essential for the formation of Perlin aldehydes. The similar reactions under neutral reaction conditions (CH3CN:H2O, 1:1, v/v) with additives, afforded the hemiacetals as major product. This methodology is a metal free approach to Perlin aldehyde synthesis and therefore having additional benefit of its use in preparation of bioactive drug molecules, where metal toxicity is the major concern. A metal free synthesis of enantiopure 2,3-dideoxy-α, β-unsaturated carbohydrate enals (Perlin aldehydes), in acidic medium using 0.5 equivalent additives (4-hydroxy-6-methyl-2-pyrone I or 4-amino coumarin II), has been reported. This efficient protocol works well for the acetylated and benzylated glycals (glucal, galactal and arabinal) and afforded Perlin aldehydes and hemiacetals in acceptable to good yields. [Display omitted] •This note highlighted the first metal free synthesis of 2,3-dideoxy-α, β-unsaturated carbohydrate enals (Perlin aldehydes).•The use of 0.5 equiv. additives improve the reaction time and yield of the desired products.•This optimised reaction protocol works well with acetylated and bezylated glycals (glucal, galactal and arabinal).•The neutral reaction conditions, CH3CN–H2O (1:1 v/v), afforded respective hemiacetals as major product.