Preparation and some reactions of benzoylated 4-deoxy-d-glycero-hex-3-enos-2-uloses

Linear Fused Pyran‐Dioxane‐Cyclohexane Tricycles: Synthesis of the Five Linkage Isomers and Ensuing Reactions

“…Silver carbonate (2.75 g, 10 mmol) and molecular sieves (4 Å , 2 g) were added to a solution of (S,S)-cyclohexanediol (1.16 g, 10 mmol) in CH 2 Cl 2 (20 mL), and the mixture was stirred for 20 min, followed by dropwise addition of (2R,6S)-4-benzoyloxy-6-(benzoyloxymethyl)-6-bromo-2H-pyran-3(6H)-one [14] (19) (2.60 g, 6 mmol) in CH 2 Cl 2 (20 mL) over 5 min. After stirring for another 15 min (TLC showed absence of starting material), the mixture was diluted with CH 2 Cl 2 (150 mL) and washed with water (3 ϫ 50 mL), dried (Na 2 SO 4 ) and taken to dryness in vacuo.…”

“…-7, C-8), 29.5, 29.8 (C-6, C-9), 63.1 (CH 2 OBz), 67.9 (C-3), 71.9 (C-2), 72.2, 72.6 (C-5a, C-9a), 78.6 (C-4), 91.9 (C4a), 96.1 (C-10a) (4 Å , 2 g) and Ag 2 CO 3 (2.76 g, 10 mmol) were added to a solution of (R,R)-1,2-cyclohexanediol (1.16 g, 10 mmol) in CH 2 Cl 2 (20 mL), and the mixture was stirred for 20 min with the exclusion of moisture and light. A solution of bromo-enolone 19 [14] (2.60 g, 6 mmol) in CH 2 Cl 2 (20 mL) was then added dropwise over 5 min. After stirring for another 15 min, TLC (n-hexane/acetone/CHCl 3 , 4:3:3) indicated the absence of 19; the mixture was filtered through kieselguhr, and the filtrate was diluted with CH 2 Cl 2 (150 mL) followed by washing with water (3 ϫ 50 mL), drying (Na 2 SO 4 ), and evaporation to dryness in vacuo.…”

Pyrano[2,3‐b]dioxanes through Bisacetalic Annulation of 2‐Ketosugars to Glycol

“…Accordingly, brief exposure of 11 at ambient temperature to tetrabutylammonium acetate in dichloromethane afforded the decalinone 22 (72%), obviously generated through elimination of benzoic acid (20 Ǟ 21) and subsequent migration of the enolic benzoyl group (arrows in 21) thereby liberating the underlying carbonyl group. The same product could also be obtained by Ag 2 CO 3 -mediated glycosidation of glucose-derived [16] enolone bromide 19 (82%) Ϫ a course not unexpected in view of the previously observed [17] formation Surprisingly, when 11 was exposed to Bu 4 NOAc in a more polar solvent such as acetonitrile (30 min, room temperature), the initial elimination of benzoic acid 20 Ǟ 21 was partially followed by a second one involving the terminal OBz group to give a dienolone ester (21 Ǟ 24), which on hemiketalization, O-8a Ǟ O-8-benzoyl shift, and protonation at the exocyclic double bond (arrows in 24) led to the dihydropyranone 25. De facto, an approximate 1:1 mixture of 22 and 25 was obtained, indicating that elimination of benzoic acid from the terminal positions in intermediate 21 was not complete under the conditions employed.…”

Sugar enolones: synthesis, reactions of preparative interest, and γ-pyrone formation

“…Chlorination or bromination of the benzoylated hydroxyglycal (12, R = H, Me, CH 2 0Bz) in a non-polar solvent proceeds with almost exclusive formation of cis-adducts (Refs. 21,22,[26][27][28], a coursethat is easily understood on the basis 1,2-benzoxonium ion intermediates. However, the factors governing the ratios of cis-adducts, i.e.…”

“…[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], thereby allowing a systematic evaluation of their synthetic potential in carbohydrate chemistry as well as an assessment of y-pyrone formation therefrom with respect to the biosynthesis of kojic acid and maltol from carbohydrate precursors.…”