Towards the synthesis of the squalestatins/zaragozic acids: Synthesis of an advanced intermediate and introduction of the C-1 sidechain

Claisen Rearrangements in Carbohydrate Chemistry

“…Recovery of approximately matching quantities of unreacted starting material indicated premature consumption of the base by N-silylation as the main side reaction, whereas no loss of the ester by b-elimination was observed. Similar experiences were reported by Rizzacasa et al when changing to a different substrate structure [70]: Benzyloxy-substituted uronate 176 gave the rearrangement products 177a and 177b in only 47% total yield, also with complete recovery of the corresponding amount of unchanged starting material (Scheme 35). Even less successful was the conversion of dibenzyloxy derivative 178a in our own study.…”

“…The varying total yields could thus be attributed to different deprotonation rates for substrates with 3,4cis or 3,4-trans ring substitution. [69,70] Scheme 36. Utilization of a uronate rearrangement product for the synthesis of zaragozic acid A [70] In the same study, information about the transition state was obtained by means of cis-pentenyl uronate 190, which gave rise to a mixture of four rearrangement products, two of which are shown in Scheme 39.…”

A Synthesis of Densely Functionalized 2,3-Dihydropyrans Using Ring-Closing Metathesis and Base-Induced Rearrangements of Dihydropyran Oxides

“…The expected products, 2,3-dihydrofurans with a hydroxy function in the allylic position, are normally prepared from carbohydrate-derived starting materials, using elimination reactions, [38] or from nucleosides. [39] These compounds are useful building blocks in the synthesis of polyether antibiotics [40,41] or C-nucleosides.…”

Synthesis and Biological Evaluation of Dichlorinated Chondramide Derivatives

“…(4 R ,5 S ,6 S )‐4‐Ethyl‐2,2,5‐trimethyl‐6‐(prop‐1‐en‐2‐yl)‐1,3‐dioxane (13): 39 TBAF (1 M in THF; 140 μL, 140 μmol) was added to a solution of ketone 12 (38.0 mg, 140 μmol) in anhydrous THF (1 mL), and the mixture was stirred for 16 h at room temperature. The resulting mixture was quenched with satd.…”