A novel and flexible synthesis of pyranose spiroacetal derivatives

Synthesis of Highly Functionalised Carbohydrate-Derived Spiroacetals by Ring-Closing Metathesis and Pauson-Khand Reaction of Ketoglycosidic Enynes

“…In this respect, it is of interest to note that the diene analogue (1-O-allyl-1-vinyl) of 7 underwent RCM very smoothly. [6] The latter observation may be explained by initial reaction of the catalyst with the less hindered O-allyl part of the molecule. In the case of 7, interaction of the catalyst with the alkene part of the molecule may be impeded by steric hindrance of the O-butynyl substituent.…”

“…Trimethylsilylation of 3 with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and BF 3 ⋅OEt 2 -promoted coupling [14] of 4 with 2-butyn-1-ol gave the desired ketoglycosidic enyne 5 in 56% yield over the two steps. Alternatively, direct coupling of 3 with 2-butyn-1-ol under the influence of the heterogeneous environmentally benign solid acid montmorillonite K-10 [6,7] in the presence of molecular sieves (4 Å ) gave 5 in 72% yield. According to the latter procedure, K-10-mediated glycosidation of the known [15] ketose 6 with 2-butyn-1-ol yielded 1-O-2-butynyl-1-vinylglucose derivative 7 in 87%.…”

“…Methanol/pyridine (1:1, 5 mL) was added and the resulting slurry was stirred for a further 5 min, then the solids were filtered off and rinsed thoroughly with EtOAc. The filtrate was concentrated in vacuo and the residue subjected to column chromatography as described for method A, giving pure 5 (0.73 g, 1.16 mmol, 72% -2-ynyl 1,2-Dideoxy-4,5,6,8-tetra-O-benzyl-α-D-gluco-oct-1-en-3-ulopyranoside (7): Keto sugar 6 [6,15] (0.44 g, 0.71 mmol) was converted into enyne 7 (0.38 g, 0.62 mmol, 87%) as described for 5 (method B). …”

“…[2] For example, a recent contribution from this laboratory revealed [3] that carbohydrates are useful starting compounds for the addition of 2-O-allyl-1-vinyl and 2-O-propargyl-1-vinyl groups which, after ring-closing metathesis (RCM) under the influence of the Grubbs catalyst (1) [4] led to functionalised fused oxacycles. Furthermore, spiroacetals of type C (see Scheme 1), which are structural elements in many natural products, [5] have proved to be readily accessible [6] from 1-O-alkenyl-substituted ketoglycosides (type B). In turn, these dienes were prepared starting from the fully protected glucopyranolactone A by Grignard addition and subsequent K-10 mediated coupling [7] with a number of unsaturated alcohols.…”

Stereoselective Synthesis of Fully Protected (S)‐1,7‐Dioxaspiro[5,5]undec‐4‐ene Derivatives of Sugars

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Keywords: Spiro compounds / Carbohydrates / Lactones / Dithiins Perbenzylated 1,7-dioxaspiro [5,5]undec-4-ene derivatives of sugars are obtained in three steps, starting from fully protected glycono-1,5-lactones. The procedure is based on the attack of a lithiated dithiinyl reagent (6) on the starting δ-glyconolactone.

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