Anomeric Reactivity-Based One-Pot Oligosaccharide Synthesis: A Rapid Route to Oligosaccharide Libraries

The assembly of an oligosaccharide library has been achieved in a practical and efficient manner employing a one-pot sequential approach. With the help of the anomeric reactivity values of thioglycosides, using a thioglycoside (mono- or disaccharide) with one free hydroxyl group as acceptor and donor coupled with another fully protected thioglycoside, a di- or trisaccharide is selectively formed without self-condensation and subsequently reacted in situ with an anomerically inactive glycoside (mono- or disaccharide) to form a tri- or tetrasaccharide in high overall yield. The approach enables the rapid assembly of 33 linear or branched fully protected oligosaccharides using designed building blocks. These fully protected oligosaccharides have been partially or completely deprotected to create 29 more structures to further increase the diversity of the library

Synthetic Applications of 3,4-Bis(trimethylsilyl)thiophene: Unsymmetrically 3,4-Disubstituted Thiophenes and 3,4-Didehydrothiophene^†^,^‡

3,4-Bis(trimethylsilyl)thiophene (1a) was synthesized by three routes:  (a) 1,3-dipolar cycloaddition; (b) modification of 3,4-dibromothiophene; and (c) intermolecular thiazole−alkyne Diels−Alder reaction. 3,4-Bis(trimethylsilyl)thiophene (1a) can function as a versatile building block for the construction of unsymmetrically 3,4-disubstituted thiophenes utilizing its stepwise regiospecific mono-ipso-substitution followed by palladium-catalyzed cross-coupling reactions. In this manner, thiophenes 15, 16, 17a−j, 19a,b, 20, 22a−c, 23a,b, 24a−d, 25a−c, and 27a−j were prepared. The thiophene-3,4-diyl dimer 28 and thiophene-3,4-diyl tetramer 29 were also realized by palladium-catalyzed self-coupling reaction of organoboroxines. The stannylthiophene 31, formed by conversion of the C−Si bond to a C−Sn bond via boroxine 26c underwent both carbonylative coupling and lithiation followed by quenching with electrophiles to afford unsymmetrically 3,4-disubstituted thiophenes 33 and 36a−c as well. Moreover, 3,4-bis(trimethylsilyl)thiophene (1a) can be used as the starting material for the generation of the highly strained cyclic cumulene 3,4-didehydrothiophene (2), whose existence was substantiated by its trapping reaction with several alkenes

Anomeric Reactivity-Based One-Pot Oligosaccharide Synthesis: A Rapid Route to Oligosaccharide Libraries

The assembly of an oligosaccharide library has been achieved in a practical and efficient manner employing a one-pot sequential approach. With the help of the anomeric reactivity values of thioglycosides, using a thioglycoside (mono- or disaccharide) with one free hydroxyl group as acceptor and donor coupled with another fully protected thioglycoside, a di- or trisaccharide is selectively formed without self-condensation and subsequently reacted in situ with an anomerically inactive glycoside (mono- or disaccharide) to form a tri- or tetrasaccharide in high overall yield. The approach enables the rapid assembly of 33 linear or branched fully protected oligosaccharides using designed building blocks. These fully protected oligosaccharides have been partially or completely deprotected to create 29 more structures to further increase the diversity of the library

Anomeric Reactivity-Based One-Pot Oligosaccharide Synthesis: A Rapid Route to Oligosaccharide Libraries

The assembly of an oligosaccharide library has been achieved in a practical and efficient manner employing a one-pot sequential approach. With the help of the anomeric reactivity values of thioglycosides, using a thioglycoside (mono- or disaccharide) with one free hydroxyl group as acceptor and donor coupled with another fully protected thioglycoside, a di- or trisaccharide is selectively formed without self-condensation and subsequently reacted in situ with an anomerically inactive glycoside (mono- or disaccharide) to form a tri- or tetrasaccharide in high overall yield. The approach enables the rapid assembly of 33 linear or branched fully protected oligosaccharides using designed building blocks. These fully protected oligosaccharides have been partially or completely deprotected to create 29 more structures to further increase the diversity of the library

Synthetic Applications of 3,4-Bis(trimethylsilyl)thiophene: Unsymmetrically 3,4-Disubstituted Thiophenes and 3,4-Didehydrothiophene^†^,^‡

3,4-Bis(trimethylsilyl)thiophene (1a) was synthesized by three routes:  (a) 1,3-dipolar cycloaddition; (b) modification of 3,4-dibromothiophene; and (c) intermolecular thiazole−alkyne Diels−Alder reaction. 3,4-Bis(trimethylsilyl)thiophene (1a) can function as a versatile building block for the construction of unsymmetrically 3,4-disubstituted thiophenes utilizing its stepwise regiospecific mono-ipso-substitution followed by palladium-catalyzed cross-coupling reactions. In this manner, thiophenes 15, 16, 17a−j, 19a,b, 20, 22a−c, 23a,b, 24a−d, 25a−c, and 27a−j were prepared. The thiophene-3,4-diyl dimer 28 and thiophene-3,4-diyl tetramer 29 were also realized by palladium-catalyzed self-coupling reaction of organoboroxines. The stannylthiophene 31, formed by conversion of the C−Si bond to a C−Sn bond via boroxine 26c underwent both carbonylative coupling and lithiation followed by quenching with electrophiles to afford unsymmetrically 3,4-disubstituted thiophenes 33 and 36a−c as well. Moreover, 3,4-bis(trimethylsilyl)thiophene (1a) can be used as the starting material for the generation of the highly strained cyclic cumulene 3,4-didehydrothiophene (2), whose existence was substantiated by its trapping reaction with several alkenes

Assembly of Oligosaccharide Libraries with a Designed Building Block and an Efficient Orthogonal Protection−Deprotection Strategy

Assembly of Oligosaccharide Libraries with a Designed Building Block and an Efficient Orthogonal Protection−Deprotection Strateg

Lewis Acids as α-Directing Additives in Glycosylations by Using 2,3-<i>O</i>-Carbonate-Protected Glucose and Galactose Thioglycoside Donors Based on Preactivation Protocol

Catalytic or stoichiometric amounts of Lewis acids were found to be very effective α-directing additives in the stereoselective glycosylations of diverse 2,3-<i>O</i>-carbonate-protected glucose and galactose thioglycoside donors by preactivation protocol. The poor stereoselectivities of 4,6-di-<i>O</i>-acetyl-2,3-<i>O</i>-carbonate protected thioglycoside donors in glycosyl coupling reactions were greatly improved, and excellent α-stereoselectivities were achieved by the addition of 0.2 equiv of BF₃·OEt₂. On the other hand, the β-selectivities of 4,6-di-<i>O</i>-benzyl-2,3-<i>O</i>-carbonate-protected thioglucoside donor toward glycosylations were reversed completely to the α-selectivities by the use of 1 equiv of SnCl₄, making the stereoselectivity controllable. Furthermore, the poor stereoselectivities of 4,6-di-<i>O</i>-benzyl-2,3-<i>O</i>-carbonate-protected thiogalactoside donor in glycosylations were also improved by using SnCl₄ as additive

Oxidant-Controlled Heck-Type <i>C</i>-Glycosylation of Glycals with Arylboronic Acids: Stereoselective Synthesis of Aryl 2-Deoxy-<i>C</i>-glycosides

Oxidative Heck-type C-glycosylations of glycals with various arylboronic acids using Pd(OAc)2 as catalyst in the presence of oxidant were developed. The corresponding ketone, enol ether, and enone types of C-glycosides were predictably obtained with benzoquinone (BQ), Cu(OAc)2/O2, and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidants, respectively. This method provides a simple, mild, and stereoselective synthesis of aryl 2-deoxy-C-glycosides

Direct C–H Trifluoromethylation of Glycals by Photoredox Catalysis

A mild, efficient, and practical transformation for the direct C–H trifluoromethylation of glycals under visible light has been reported for the first time. This reaction employed fac-Ir³⁺(ppy)₃ as the photocatalyst, Umemoto’s reagent as the CF₃ source, and a household blue LED or sunlight as the light source. Glycals bearing both electron-withdrawing and -donating protective groups performed this reaction smoothly. This visible light-mediated trifluoromethylation reaction was highlighted by the trifluoromethylation of the biologically important Neu2en moiety

Nitro-polyols via Pyridine Promoted CC Cleavage of 2‑Nitroglycals. Application to the Synthesis of (−)-Hyacinthacine A1

A mild and convenient transformation for the synthesis of nitro-polyols is described. The nitro-polyol derivatives were prepared either from 2-nitroglycals via a pyridine-promoted scission of the carbon–carbon double bond or from glycals via a sequential nitration–scission procedure. The generated nitro-polyols could undergo a stereoselective Michael addition reaction. The utility of the addition products was exemplified by the concise synthesis of (−)-hyacinthacine A1 and 7a-<i>epi</i>-(−)-hyacinthacine A1