InCl3-CH3CN-H2O: an efficient catalyst-solvent combination for the synthesis of Perlin aldehydes and related compounds. Application in the synthesis of unnatural l-azasugars

InCl₃-CH₃CN-H₂O has been found to be an efficient catalyst-solvent combination for the synthesis of Perlin aldehydes and related compounds. While acetylated glycals afforded the Perlin aldehydes directly with InCl₃ and water, benzylated glycals on the other hand provided the hemiacetals under identical condition. The methodology reports a non-mercurial approach to Perlin aldehydes. Noteworthy is that this reaction is more facile as well as highly selective with glycals possessing a hydroxyl as a leaving group than with a benzyloxy group. Extension of this reaction to 2-C-hydroxymethyl glycals resulted in the formation of the corresponding hemiacetals, which were further transformed in to unsaturated azasugars with an exo-methylene group at C-2 position. Glycosidase inhibition studies reveal that these compounds display selectivity in inhibiting glucosidases rather than galactosidases.     

Approaches to the synthesis of CF2-analogues of 2-deoxy-2-aminoglycosides

The preparation of a fluorinated C-glycosidic analogue of a 2-deoxy-2-acetamido-d-altrose is described. The synthetic sequence involves the addition of a difluoroenoxysilane to a d-glucal, an epoxidation of the resulting unsaturated CF₂-glycoside and a ring-opening reaction with TMSN₃. An Overman rearrangement of the unsaturated intermediate is also described.     

Regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles via three-component coupling of secondary alcohols, TMSN3 and alkynes

1,4-Disubstituted 1,2,3-triazoles are obtained in excellent yields via a three-component coupling of secondary alcohols, alkynes and trimethylsilyl azide (TMSN₃). This one-pot reaction occurs through in situ generation of an azide from the alcohol and TMSN₃, followed by 1,3-dipolar cycloaddition of the terminal alkyne to afford the corresponding disubstituted triazoles.     

Synthesis of C-2 methylene glycosides from C-2 propargyloxymethyl glycals exploiting the alkynophilicity of AuCl3

C-2 Methylene glycosides were synthesized from C-2 propargyloxymethyl glycals in a stereoselective manner using a catalytic quantity of AuCl₃. The Au-catalyzed reaction was explored using various aglycones. The current protocol enables the preparation of C-2 methylene glycosides, tolerates diverse functional groups and is fast, catalytic and mild.     

An efficient synthesis of 1-cyano-2,3-unsaturated sugars via the reaction of glycals with Et2AlCN

The reaction of glycals 1a-d with Et₂AlCN in benzene at room temperature leads to formation of the corresponding 1-cyano-2,3-unsaturated sugars 2a-d and 3a-d in good to excellent yields.     

An efficient synthesis of 5-substituted 1H-tetrazoles via B(C6F5)3 catalyzed [3+2] cycloaddition of nitriles and sodium azide

A simple and efficient protocol is developed for the synthesis of 5-substituted 1H-tetrazole derivatives from various nitriles and sodium azide (NaN₃) via [3+2] cycloaddition reaction using B(C₆F₅)₃ as a catalyst. The present synthetic method displayed significant advantages such as low catalyst loading, mild reaction conditions, low toxicity, easy work-up, high yields, and compatibility with other functional groups.     

(NH4)2Ce(NO3)6 as an inexpensive,eco-friendly,efficient catalyst for the synthesis of 5-substituted 1-H tetrazoles from nitriles

Ceric ammonium nitrate (CAN) is found to be a suitable, inexpensive, and effective non-toxic catalyst for a smooth (3+2) cycloaddition of organic nitriles with NaN₃ to afford 5-substituted 1H-tetrazoles in excellent yields. Shorter reaction times, easy work-up, and substantial and pure product formation are the key advantages of the present method.     

Reaction of N-fluoropyridinium fluoride with isonitriles and TMSN3: a convenient one-pot synthesis of tetrazol-5-yl pyridines

Reaction of N-fluoropyridinium fluoride generated in situ with a series of isonitriles and TMSN₃ led to the formation of the corresponding tetrazol-5-yl pyridines in good yields (37-84%). A similar reaction sequence for quinoline yielded the respective derivatives of 2-quinoline. The proposed reaction mechanism involves the intermediate formation of a highly reactive carbene species.     

A simple,efficient thermally promoted protocol for Huisgen-click reaction catalyzed by CuSO4·5H2O in water

A thermally promoted and CuSO₄-catalyzed new version of the Huisgen-click reaction is presented in this Letter. Notably, this protocol was suitable not only for the reactions between organic azides and alkynes, but also for one-pot three-component reactions among alkyl halides, NaN₃, and alkynes.     

Stereoselective synthesis of 2-C-methylene glycosides and disaccharides via direct allylic substitution of hydroxy group in benzylated glycals

InCl₃ efficiently catalyzes allylic substitution of the hydroxy group of 2-C-hydroxymethyl glycals to afford a diversity of 2-C-methylene alkyl and aryl glycosides as well as disaccharides in high yields. This protocol surpasses the existing methods for the synthesis of 2-C-methylene glycosides as it obviates the need for functionalizing the allylic hydroxy group of glycals. The interest of this methodology relies on the extremely mild conditions required even with a free hydroxyl group at the allylic position of the glycals and that too only with a catalytic amount of InCl₃. The reaction is fast (30 min.), stereoselective and is compatible with a variety of oxygenated nucleophiles including those possessing acid-labile groups. A mechanistic investigation on the direct formation of an α,α-(1→1)linked disaccharide derivative from 2-C-hydroxymethyl galactal reveals that the reaction proceeds through a domino Ferrier rearrangement followed by a facile 1,3-alkoxy migration.     

A highly regioselective azidolysis of 2,3-epoxy amines: an unexpected [Ti(O-i-Pr)2(N3)2] mediated C-2 opening

The Lewis acid-catalysed regioselective azidolysis of 2,3-epoxy amines has been investigated. The results obtained demonstrated that using TMSN₃ as a source of azide, the appropriate choice of Lewis acid allowed to direct the regiochemistry of the ring opening. The present methodologies provide a powerful tool in organic synthesis for the preparation of diaminoalcohol moieties.     

Indium(III) triflate catalyzed tandem azidation/1,3-dipolar cycloaddition reaction of ω,ω-dialkoxyalkyne derivatives with trimethylsilyl azide

The azidation reaction of dialkyl acetal derivatives with trimethylsilyl azide (TMSN₃) was efficiently catalyzed by 1-5 mol % of In(OTf)₃. The major product differed depending on the substrate structure and molar ratio of TMSN₃, that is, aliphatic acetals provided α-azido ether derivatives, while aromatic acetal (benzaldehyde dimethyl acetal) provided gem-diazide, respectively. Furthermore, novel tandem azidation/1,3-dipolar cycloaddition reaction using alkynyl acetal derivatives gave bicyclic triazolo-heterocyclic compounds, recognized as chemically modified aza-sugar analogues, in high yields under mild conditions.     

A study of the mechanism of the azidophenylselenylation of glycals

Chemical and physicochemical studies of homogeneous azidophenylselenylation of glycols with diacetoxyiodobenzene, trimethylsilyl azide, and diphenyl diselenide in dichloromethane revealed that the most probable key reaction step is the formation of phenylselenyl azide, an azide radical donor. A method for azidophenylsulfenylation of glycals was proposed.     

Reactions of glycals with xenon fluoride: an improved synthesis of 2-deoxy-2-fluorosaccharides

The 1,2-double bond in acetylated glycals has been fluorinated with XeF₂ in the presence of BF₃ to give 1,2-deoxy-1,2-difluorosaccharides. A mechanism for this reaction has been proposed. This method represents an improvement in the synthesis of 2-deoxy-2-fluorosaccharides.     

One-step synthesis of pentavalent triphenylantimony derivatives Ph3Sb(OSiR3)2, Ph3Sb(OCH2CH2)2NH and Ph3Sb(OCH2CH2NMe2)2: X-ray molecular structure of Ph3Sb(OSiMe3)2

Pentavalent bis(triorganosiloxy)triphenylantimony derivatives, Ph₃Sb(OSiR₃)₂ (R = Me, Ph), were synthesized by reaction of triphenylantimony with trimethyl- or triphenylsilanol in the presence of tert-butylhydroperoxide by the mild reaction conditions (0-5 °C, 2 h). The reaction of triphenylantimony with diethanolamine in the presence of tert-butylhydroperoxide gave the cyclic compound Ph₃Sb(OCH₂CH₂)₂NH. The mixture of Ph₃SbO and Ph₃Sb(OCH₂CH₂NMe₂)₂ was obtained by the reaction of triphenylantimony with 2-(N,N-dimethylamino)ethanol in the presence of tert-butylhydroperoxide.     

Enantioselective desymmetrization of meso-N-(heteroarenesulfonyl)aziridines with TMSN3 catalyzed by chiral Lewis acids

A catalytic enantioselective desymmetrization of meso-N-(heteroarenesulfonyl)aziridines with TMSN₃ using chiral Lewis acids afforded products with high enantioselectivity. As proof of the utility of this procedure, the precursor of selective κ-opioid agonist (1S,2S)-(−)-U-50,488 was synthesized.     

A facile and rapid route for the synthesis of novel 1,5-substituted tetrazole hydantoins and thiohydantoins via a TMSN3-Ugi/RNCX cyclization

This Letter describes novel methodology for the rapid assembly of new and biologically appealing 1,5-substituted tetrazole-hydantoins and thiohydantoins. The product of a TMSN₃-Ugi multi-component reaction is treated with an excess of isocyanate or isothiocyanate to generate the final scaffold in moderate to good yields. The applicability of this solution phase methodology to the preparation of a small collection of compounds is discussed.     

On the PdCl2-catalyzed synthesis of allylic azides and allylic sulfonamides from homoallylic alcohols

According to experimental and literature data, the one-pot formation of allylic azides or sulfonamides from catalytic amounts of PdCl₂, homoallylic alcohols and TMSN₃ or TsNH₂ occurs through CC migration followed by regioselective nucleophilic addition on the Pd^II-activated CC bond and β-OH elimination.     

MgO－B2O3－MgCl2－H2O体系与盐酸滴定反应的研究

ＭｇＯ－Ｂ２Ｏ３－ＭｇＣｌ２－Ｈ２Ｏ是含硼盐湖日晒浓缩盐卤的典型体系，它与盐酸反应生成硼酸，是从天然浓缩盐卤中制取硼酸的工艺基础，以量热滴定法和ＰＨ滴定法研究该反应，结果表明，析出硼酸的反应分两步进行；合成盐卤中硼酸盐可用ＭｇＢ２ｎＯ３Ｎ＋１（ｎ＝１，２，３）综合统计形式来表示；天然浓缩盐卤中硼酸盐可以用四硼酸镁的统计形式进行表示。     

Synthesis of and Glycosidation by 2-Deoxy-2-Fluoro-D-Mannopyranose

Abstract

With the increased biochemical interests of fluorocarbohydrates, several approaches have been establised toward the synthesis of 2-deoxy-2-fluorocarbohydrates by taking advantage of the ease of the addition reaction to readily available peracetylated glycals by employing either CF₃OF,¹ F₂,² or XeF₂,³ More stereochemically controlled approaches utilize the epoxide opening reaction with KHF₂ ⁴ or the displacement of 2-0-triflate by CsF.⁵