Cascade Rearrangements of Polyunsaturated Sugars: A Novel Approach to the Synthesis of Oligosaccharide Mimetics

Synthesis of the Three Most Expensive l-Hexose Thioglycosides from d-Glucose

“…The hydrogen iodide elimination was tested with three reagents most commonly used in the literature, including NaH, 39 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), [40][41][42][43] and AgF. 44 The expected 5,6-unsaturated compound 20 was formed in the NaH-induced elimination reaction in a low yield (18%).…”

Synthesis of the Three Most Expensive l-Hexose Thioglycosides from d-Glucose

“…The hydrogen iodide elimination was tested with three reagents most commonly used in the literature, including NaH, 39 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), [40][41][42][43] and AgF. 44 The expected 5,6-unsaturated compound 20 was formed in the NaH-induced elimination reaction in a low yield (18%).…”

Synthesis of Four Orthogonally Protected Rare l-Hexose Thioglycosides from d-Mannose by C-5 and C-4 Epimerization

“…Our synthetic design requires 5,6-unsaturated pyranosides as key intermediates on which hydroboration/oxidation can be performed. A well-documented method for preparing the pyranosyl exocyclic alkene is the base-mediated elimination of the corresponding 6-deoxy-6-iodo-glycosides, for which silver(I) fluoride (AgF) [ 68 ], potassium tert -butoxide ( t -BuOK) [ 69 ], sodium hydride (NaH) [ 70 ], and 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) [ 71 , 72 , 73 , 74 ] reagents are the most commonly used. However, monitoring of this dehydroiodination step is notoriously difficult, and it often suffers from unwanted side reactions [ 65 , 66 ] that may be exacerbated in the presence of base-sensitive ester protecting groups.…”

Synthesis of the Three Most Expensive l-Hexose Thioglycosides from d-Glucose

“…The hydrogen iodide elimination was tested with three reagents most commonly used in the literature, including NaH, 39 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), [40][41][42][43] and AgF. 44 The expected 5,6-unsaturated compound 20 was formed in the NaH-induced elimination reaction in a low yield (18%).…”

Synthesis of Four Orthogonally Protected Rare l-Hexose Thioglycosides from d-Mannose by C-5 and C-4 Epimerization

“…Our synthetic design requires 5,6-unsaturated pyranosides as key intermediates on which hydroboration/oxidation can be performed. A well-documented method for preparing the pyranosyl exocyclic alkene is the base-mediated elimination of the corresponding 6-deoxy-6-iodo-glycosides, for which silver(I) fluoride (AgF) [ 68 ], potassium tert -butoxide ( t -BuOK) [ 69 ], sodium hydride (NaH) [ 70 ], and 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) [ 71 , 72 , 73 , 74 ] reagents are the most commonly used. However, monitoring of this dehydroiodination step is notoriously difficult, and it often suffers from unwanted side reactions [ 65 , 66 ] that may be exacerbated in the presence of base-sensitive ester protecting groups.…”

Synthesis of the Three Most Expensive l-Hexose Thioglycosides from d-Glucose

“…The hydrogen iodide elimination was tested with three reagents most commonly used in the literature, including NaH, 39 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), [40][41][42][43] and AgF. 44 The expected 5,6-unsaturated compound 20 was formed in the NaH-induced elimination reaction in a low yield (18%).…”

Synthesis of Four Orthogonally Protected Rare l-Hexose Thioglycosides from d-Mannose by C-5 and C-4 Epimerization

“…Our synthetic design requires 5,6-unsaturated pyranosides as key intermediates on which hydroboration/oxidation can be performed. A well-documented method for preparing the pyranosyl exocyclic alkene is the base-mediated elimination of the corresponding 6-deoxy-6-iodo-glycosides, for which silver(I) fluoride (AgF) [ 68 ], potassium tert -butoxide ( t -BuOK) [ 69 ], sodium hydride (NaH) [ 70 ], and 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) [ 71 , 72 , 73 , 74 ] reagents are the most commonly used. However, monitoring of this dehydroiodination step is notoriously difficult, and it often suffers from unwanted side reactions [ 65 , 66 ] that may be exacerbated in the presence of base-sensitive ester protecting groups.…”