Thioarylation of 6-Amino-2,3,6-trideoxy-d-manno-oct-2-ulosonic Acid (IminoKdo): Access to 3,6-Disubstituted Picolinates and Mechanistic Insights.

In this work, we present a metal-free coupling protocol for the regio- and stereoselective C3-thioarylation of 6-amino-2,3,6-trideoxy-d-manno-oct-2-ulosonic acid (iminoKdo). The developed procedure enables the coupling of electron-rich, electron-deficient, and hindered arylthiols, providing a series of C3-modified iminoKdo derivatives in moderate to good yields. Elucidation of active species through controlled experimental studies and time-lapse 31 P NMR analysis provides insights into the reaction mechanism. We demonstrate that, following a tandem Staudinger/aza-Wittig reaction of an azido-containing keto ester, an inseparable equimolar mixture of imine/enamine is formed. The enamine then undergoes a Stork-like nucleophilic attack with the in situ-formed disulfide reagent, resulting in the formation of the coupling products. Additionally, we describe a rarely reported acid-promoted aromatization of the C3-thioarylated iminoKdo skeleton into 3,6-disubstituted picolinates, which are reminiscent of dichotomines.

Atroposelective PIII /PV =O Redox Catalysis for the Isoquinoline-Forming Staudinger-aza-Wittig Reaction.

Herein, we describe the feasibility of atroposelective PIII /PV =O redox organocatalysis by the Staudinger-aza-Wittig reaction. The formation of isoquinoline heterocycles thereby enables the synthesis of a broad range of valuable atropisomers under mild conditions with enantioselectivities of up to 98 : 2 e.r. Readily prepared azido cinnamate substrates convert in high yield with stereocontrol by a chiral phosphine catalyst, which is regenerated using a silane reductant under Brønsted acid co-catalysis. The reaction provides access to diversified aryl isoquinolines, as well as benzoisoquinoline and naphthyridine atropisomers. The products are expeditiously transformed into N-oxides, naphthol and triaryl phosphine variants of prevalent catalysts and ligands. With dinitrogen release and aromatization as ideal driving forces, it is anticipated that atroposelective redox organocatalysis provides access to a multitude of aromatic heterocycles with precise control over their configuration.

One-Pot Sequence of Staudinger/aza-Wittig/Castagnoli-Cushman Reactions Provides Facile Access to Novel Natural-like Polycyclic Ring Systems.

Realization of the one-pot Staudinger/aza-Wittig/Castagnoli-Cushman reaction sequence for a series of azido aldehydes and homophthalic anhydrides is described. The reaction proceeded at room temperature and delivered novel polyheterocycles related to the natural product realm in high yields and high diastereoselectivity. The methodology has been extended to three other cyclic anhydrides. These further unravel the potential of the Castagnoli-Cushman reaction in generating polyheterocyclic molecular scaffolds.

Cesium cation templated selective synthesis of a "cone-shaped" sugar macrotricyclic cryptand: A dual anion-cation molecular recognition of potassium tartrate.

Cesium templated Staudinger-aza-Wittig tandem reaction (S.A.W.) has been used in the synthesis of a bis-diazacrown-bis-cellobiosyl-tetra-ureido cryptand. A novel macrotricyclic compound having a "cone-shaped" configuration was selectively obtained. Additionally, first results on potential recognition properties of the cryptand are also given.

Synthesis of bi-/tricyclic azasugars fused thiazinan-4-one and their HIV-RT inhibitory activity.

Novel bi-/tricyclic azasugars fused thiazinan-4-one were conveniently synthesized by the tandem Staudinger/aza-Wittig/cyclization reaction under microwave radiation. The aryl group (phenyl or pyridyl) in mercaptan acid had an important effect on the formation of the diastereomers of the tricyclic hybrids 12b-15b. The new bi/tricyclic azasugars 3a-8a, 4b, 6b, 8b and the known ones 2a, 2b were examined for their HIV reverse transcriptase (RT) inhibitory activities. The result showed that compounds 2a-b, 4a, 4b, 5a, and 6a could effectively inhibit RT activity. Among them, the tricyclic azasugar 5a was the best one with the IC50 value of 0.49 µM. Structure-activity relationship analysis suggested that the phenyl group in the tricyclic azasugars was benefit for their anti-HIV RT activity.

Concise synthesis of C-1-cyano-iminosugars via a new Staudinger/aza Wittig/Strecker multicomponent reaction strategy.

A new Staudinger/aza Wittig/Strecker multicomponent reaction sequence to C-1-cyano iminoalditols has been developed. When applied to 5-azidodeoxy-d-xylose and -d-glucose as substrates the method leads smoothly in good yield and with excellent stereoselectivity to respectively, 1,5-dideoxy-1,5-imino-d-idurono nitrile and 2,6-didesoxy-2,6-imino-d-glycero-d-ido-heptononitrile.

Capped guanidino-α-cyclodextrin first synthesis based on intramolecular Staudinger-Aza-Wittig (SAW) reaction.

An intramolecularly promoted SAW reaction between a phosphinimide and an isocyanate intermediate led to an original bridged trisubstituted ((A,C),E)-α-cyclodextrin. The latter was in a second step converted into a new capped (ACE)-(guanidino)-α-cyclodextrin.

One-pot sequential synthesis of isocyanates and urea derivatives via a microwave-assisted Staudinger-aza-Wittig reaction.

A fast and efficient protocol for the synthesis of N,N'-disubstituted urea derivatives from alkyl halides and primary or secondary amines has been developed. The synthetic pathway combines nucleophilic substitutions and a Staudinger-aza-Wittig reaction in the presence of polymer-bound diphenylphosphine under 14 bar of CO2 pressure and has been performed in a one-pot two-step process. The protocol has been optimized under microwave irradiation and the scale-up experiment has been conducted under conventional conditions in a Parr reactor. The final compounds were isolated after simple filtration in almost quantitative overall yields which makes this procedure facile and rapid to execute.

Synthesis of Isothiocyanates: An Update.

Isothiocyanates (ICTs) are a group of molecules that can be used for many different purposes, they exhibit anticancer, antimicrobial, antibiotic, and anti-inflammatory properties. The synthesis of isothiocyanates has been a focus of many researchers for nearly the past 100 years. One of the most common synthetic methods is to form a dithiocarbamate salt, either as the first step or in situ, and then treat the salt with a desulfurization agent to reach the isothiocyanate. There are many different desulfurization agents available. Among these, there are eleven in particular that will be discussed in this short review, namely thiophosgene, lead nitrate, ethyl chloroformate, hydrogen peroxide, triphosgene, iodine, cobalt, copper, sodium persulfate, claycop, and tosyl chloride. There are four additional particular methodologies that stand out from the literature available on this topic that will be covered, namely the production of isothiocyanates from hydroximoyl chlorides, via elemental sulfur, microwave-assisted synthesis, and through the tandem Staudinger/aza-Wittig reactions.

Synthesis of tetracyclic azasugars fused benzo[e][1,3]thiazin-4-one by the tandem Staudinger/aza-Wittig/cyclization and their HIV-RT inhibitory activity.

Azasugar aldehydes 6a and 6b containing azido groups were prepared from D-mannose. Three novel tetracyclic azasugars fused benzo[e][1,3]thiazin-4-one 9a-1, 9a-2 and 9a-3 were conveniently synthesized from 6a by the tandem intramolecular Staudinger/aza-Wittig/cyclization reaction under microwave radiation. Two unexpected elimination compounds 8b-1 and 8b-2 were achieved as the main products from 6b in the same processes. The newly synthesized azasugars were examined for their HIV reverse transcriptase (RT) inhibitory activities. The results showed that all the tested compounds could effectively inhibit RT activity. Among them, compound 8b-1 with the protective group (isopropylidene group) was the best one with the IC50 value of 0.76 µM. The structure activity relationship analysis suggested that improvement of the molecular hydrophilicity might be beneficial for their anti-HIV RT activities.

Synthesis of seven-membered iminosugars fused thiazolidin-4-one and benzthiazinan-4-one and their HIV-RT inhibitory activity.

Novel seven-membered iminosugars fused thiazolidin-4-one and benzthiazinan-4-one were conveniently synthesized by the tandem Staudinger/aza-Wittig/cyclization reaction under microwave radiation. Benzoyl group (Bz) migrations were found in the synthesis of 8c and 9b using D-galactoside or D-mannoside as starting materials, respectively, which was suggested by HMBC and X-ray. The new bi/tricyclic iminosugars 3~4(a-d) and 5(b-d) were examined for their HIV reverse transcriptase (RT) inhibitory activities. The result showed that all compounds except 5b could effectively inhibit RT activity. Among them, compounds 3c and 4c were the best ones with the IC50 values of RT inhibitory activities of 2.11 µM and 2.73 µM, respectively. Structure-activity relationship analysis suggested that the phenyl group in the tricyclic azasugars was beneficial for their anti-HIV RT activity.

The Staudinger/aza-Wittig/Grignard reaction as key step for the concise synthesis of 1-C-Alkyl-iminoalditol glycomimetics.

The scope of a one-pot tandem approach for the synthesis of C-1 alkyl iminoalditol derivatives with a Staudinger/aza-Wittig/Grignard cascade has been evaluated. The reaction conditions have been optimized for two azidodeoxy aldose substrates and a range of Grignard reagents. The nature of both, substrate as well as nucleophile, was found to control the stereoselectivity of the alkyl addition to the cyclic iminium intermediate at position C-1. This approach enabled the synthesis of a collection of C-alkyl iminoalditols, which were biologically evaluated as inhibitors against a set of standard glycoside hydrolases. All compounds were found to exhibit highly selective inhibition of ß-glucosidase activity.

Synthesis of new saccharide azacrown cryptands.

New cryptands including bis-azacrown and saccharidic moieties in their structure were prepared in several steps by applying Staudinger-aza-Wittig reaction (SAW). Syntheses have been started from cheap, easily available commercial compounds such as D-glucose, D-cellobiose and D-lactose subsequently transformed into their derivatives in fairly good yields (60-65%) and suitable to give desired final cryptands by direct SAW coupling reactions.