Ylidenebutenolide mycotoxins. Concise syntheses of patulin and neopatulin from carbohydrate precursors

Synthesis and Biological Evaluation of Sugars Containing α,β‐Unsaturated γ‐Lactones

“…A salient feature of the 1 H NMR spectra of 15 and 16 is the two separate sets of AB systems for the five-membered ring lactone unit, assigned for 5Јa-H, 5Јb-H, and 6a-H, 6b-H, the latter shifted upfield. The presence of the signals at 174.8 and 175.1 for the carbonyl groups of 15 and 16, respectively, in their 13 C NMR spectra confirmed the lactone skeleton. Our proposed configuration for the stereogenic centre (C-5) of the formed lactone is based on the assumption that the nucleophilic attack of the Reformatsky reagent to 5-6 should occur from the less hindered face of the carbonyl group.…”

“…However, when the ribo-hexofuranos-5-ulose derivatives 7-8 were used as starting materials, the corresponding Wittig reaction provided mainly the formation of the (E) adducts, the spontaneous cyclization of which gave the α,β-unsaturated-γ-lactones 13, 14 in 47 % and 49 % yield, respectively. The carbonyl groups of the butenolide moeties were confirmed by the signals at δ = 173.3 in their 13 C NMR spectra. In the 1 H NMR spectra, olefinic protons give rise to signals at δ = 6.06 and 6.12, respectively, and as a consequence of lactonization, chemical shifts values for 4-H around δ = 4.85 are much smaller than those observed for their acyclic (Z)-aducts 11 and 12, which were isolated in only 12 and 11 % yield, respectively.…”

“…The 1 H NMR spectra of the α-hydroxy ketone products show AB-system patterns for 6a-H, 6b-H, with geminal coupling constants from 20.2 to 20.5 Hz. The carbonyl groups of 5-8 give rise to characteristic signals in the 13 C-NMR spectra (δ = 208.2, 208.2, 207.1, and 207.3, respectively) and show IR band absorptions at 1725 and 1730 cm -1 . The lower yield obtained for the ribo derivatives may result from dimerization of the α-hydroxy ketones, which must depend on the stereochemistry at C-3, as suggested in the literature.…”

“…[11,12] With respect to sugar-fused α,β-unsaturated γ-lactones, some literature reports describe their use for the preparation of bioactive natural products and branched-chain sugars. [13,14] We have recently demonstrated an effective route to access various butenolides fused to pento-and hexopyranoses. [15] The strategy is based on the Wittig olefination of furanos-3-uloses containing acid-labile 5-O-or 5,6-di-Oprotecting groups, followed by acid hydrolysis.…”

Titanium Silicalite 1 (TS‐1) Catalyzed Oxidative Transformations of Furan Derivatives with Hydrogen Peroxide

“…For example, although the NBS and peroxyacid mediated reactions appear to offer simple procedures, it was found that these methods are unreliable and unsuitable for all but very small-scale work. [19] On the other hand, the 9.5 79 20…”