One-Pot Synthesis of 2-C-Branched Glycosyl Triazoles by Integrating 1,2-Cyclopropanated Sugar Ring-Opening Azidation and CuAAC Reaction

A series of 2-C-branched glycosyl triazoles including triazole-tethered oligosaccharides and glycopeptides were synthesized in one pot from 1,2-cyclopropanated sugars or 2'-acetonyl-2-O-Ts-C-furanosides, NaN₃, and alkynes using PEG-400 as a single solvent. Nucleophilic ring-opening azidation of 1,2-cyclopropanated sugars (or 2'-acetonyl group 1,2-migration-azidation of C-furanosides) obtained glycosyl azides, which upon reaction with alkynes under CuAAC conditions achieved glycosyl triazoles in good yields and high stereoselectivity without the need to change the solvent and isolate any intermediates.

A Novel Method to Construct 2-Aminobenzofurans via [4 + 1] Cycloaddition Reaction of In Situ Generated Ortho-Quinone Methides with Isocyanides

A new approach for the synthesis of 2-aminobenzofurans has been described via Sc(OTf)₃ mediated formal cycloaddition of isocyanides with the in situ generated ortho-quinone methides (o-QMs) from o-hydroxybenzhydryl alcohol. Notably, as a class of readily available and highly active intermediates, o-QMs were first used in the construction of benzofurans. This [4 + 1] cycloaddition reaction provides a straightforward and efficient methodology for the construction of 2-aminobenzofurans scaffold in good yield (up to 93% yield) under mild conditions.

Lewis acid triggered N-alkylation of sulfoximines through nucleophilic ring-opening of donor-acceptor cyclopropanes: synthesis of γ-sulfoximino malonic diesters

Scandium triflate (Sc(OTf)₃) catalyzed, mild, and regioselective ring-opening reaction of donor-acceptor (D-A) cyclopropanes has been developed using sulfoximines for the synthesis of γ-sulfoximino malonic diesters. This protocol allows the synthesis of different N-alkyl sulfoximines in good to excellent yields (up to 94%) with broad functional group tolerance. In this process, N-H and C-C bonds are cleaved to form new C-N and C-H bonds. The feasibility of this method is supported by a gram-scale reaction and synthetic elaboration of the obtained product.

1, 2-trans-Stereoselective 7-O-Glycosylation of Flavonoids with Unprotected Pyranoses by Mitsunobu Reaction

The glycosylation of protecting-group-free pyranoses with flavonoids to generate flavonoid O-glycosides under Mitsunobu conditions was reported. The methodology allows to prepare a wide range of natural 7-flavonoid O -glycosides and their derivatives from commercially available chemicals in good to excellent yields with exclusive 1,2- trans -stereoselectivity regardless the anomeric configuration of employed pyranoses. The highly regioselective glycosylation was also achieved among different types of hydroxyl groups on the glycosyl acceptors.

Reactions of Allylmagnesium Reagents with Carbonyl Compounds and Compounds with C═N Double Bonds: Their Diastereoselectivities Generally Cannot Be Analyzed Using the Felkin-Anh and Chelation-Control Models

This review describes the additions of allylmagnesium reagents to carbonyl compounds and to imines, focusing on the differences in reactivity between allylmagnesium halides and other Grignard reagents. In many cases, allylmagnesium reagents either react with low stereoselectivity when other Grignard reagents react with high selectivity, or allylmagnesium reagents react with the opposite stereoselectivity. This review collects hundreds of examples, discusses the origins of stereoselectivities or the lack of stereoselectivity, and evaluates why selectivity may not occur and when it will likely occur.

An efficient and facile strategy for trifluoromethylation and perfluoroalkylation of isoquinolines and heteroarenes

An effective and regioselective strategy for trifluoromethylation and perfluoroalkylation of isoquinolines and heteroarenes was developed.

A facile method for the synthesis of fused perhydropyrano[2,3-b]pyrans promoted by Yb(OTf)3

A stereospecific three-component domino reaction between glycals, alkylidene malonate and aldehydes catalyzed by Yb(OTf)3 is described. Multi-substituted cis-fused perhydropyrano[2,3-b]pyran derivatives were obtained with high diastereoselectivity.

[3 + 3]-Cycloaddition of Donor-Acceptor Cyclopropanes with Nitrile Imines Generated in Situ: Access to Tetrahydropyridazines

Donor-acceptor cyclopropanes are reacted under the influence of a Lewis acid with hydrazonyl chlorides to afford tetrahydropyridazines. Formally, this transformation can be regarded as a [3 + 3]-cycloaddition of three-membered rings and nitrile imines generated in situ. This efficient method provides fast access to a variety of structurally diverse pyridazine derivatives. The structure of a typical product was confirmed by X-ray crystallography.

Zn(OTf)2 promoted rearrangement of 1,2-cyclopropanated sugars with amines: a convenient method for the synthesis of 3-polyhydroxyalkyl-substituted pyrrole derivatives

A rearrangement reaction of 1,2-cyclopropanated sugars with alkylamines or arylamines promoted by Zn(OTf)2 is described. The method offers a series of 3-polyhydroxyalkyl-substituted pyrrole derivatives with multiple chiral centers in moderate to excellent yields. The epimerization is achieved by inverting the stereochemistry at the free hydroxyl group of the resulting pyrrole, which would give access to many more possible stereoisomers.

Stereospecific [3+2] cycloaddition of 1,2-cyclopropanated sugars and ketones catalyzed by SnCl4: an efficient synthesis of multi-substituted perhydrofuro[2,3-b]furans and perhydrofuro[2,3-b]pyrans

An efficient stereospecific [3+2] cycloaddition of 1,2-cyclopropanated sugars and ketones catalyzed by SnCl₄ is described.

A neighboring group participation strategy: direct and highly diastereoselective synthesis of 2-substituted and 2,2-bisubstituted perhydrofuro[2,3-b]pyran derivatives

A highly diastereoselective synthesis method for 2-substituted and 2,2-bisubstituted perhydrofuro[2,3-b]pyran derivatives from 2-C-branched sugars via a neighboring group participation strategy was developed.