Oxidative [3+2]-annulation of nitroalkenes and azolium ylides in the presence of Cu(II): efficient synthesis of [5,5]-annulated N-fused heterocycles

A facile synthesis of [5,5]-annulated N-fused heterocycles – pyrrolo[2,1-b]thiazoles and pyrrolo[1,2-b]indazoles via Cu(II)-mediated oxidative [3+2]-annulation between nitroalkenes and azolium ylides was developed. The reaction proceeds in mild conditions with copper (II) trifluoroacetate/2,6-lutidine system as a promoter. The method is applicable to a broad range of nitroalkenes and azolium salts, providing target N-fused heterocycles in moderate to good yields. In the case of α-fluoronitroalkenes unique fluorinated derivatives were accessed via this methodology.

Overhaul of the reducing ability of Breslow-type derivatives and implications for carbene-catalyzed radical reactions.

We report the synthesis of acyl azolium salts stemming from thiazolylidenes CNS, triazolylidenes CTN, mesoionic carbenes CMIC and the generation of their corresponding radicals and enolates, covering about 60 Breslow-type derivatives. This study highlights the role of additives in the redox behavior of these compounds and unveils several critical misconceptions about radical transformations of aldehyde derivatives under N-heterocyclic carbene catalysis. In particular, the reducing ability of enolates has been dramatically underestimated in the case of biomimetic CNS. In contrast with previous electrochemical studies, we show that these catalytic intermediates can transfer electrons to iodobenzene within minutes at room temperature. Enols derived from CMIC are not the previously claimed super electron donors, although enolate derivatives of CNS and CMIC are powerful reducing agents.

Reactions Catalyzed by 2-Halogenated Azolium Salts: From Halogen-Bond Donors to Brønsted-Acidic Salts

Our research group has developed a variety of organocatalysts, especially bi- and multi-functional hydrogen-bond (HB)-donor catalysts. Since 2013, we have become interested in halogen-bond (XB) interactions in organic synthesis, and we have focused on the development of organocatalysts using XBs. Although it is difficult to develop otherwise inaccessible transformations using XBs as the primary interaction, we found several unique reactions that use XB interactions in combination with co-catalysts such as trimethylsilyl iodide, Proton Sponge, and Schreiner’s thiourea. During the synthesis of various 2-iodoazolium salts that can serve as XB donors, a ‘protonated’ 2-iodoazolium salt (a Brønsted-acidic salt) was unexpectedly obtained instead of the corresponding ‘alkylated’ 2-iodoazolium salt (XB donor). The obtained Brønsted-acidic salt is unprecedentedly effective for the N-glycosylation of amides. This account summarizes our findings in this area to date.1 Introduction2 Organoiodine-Compound-Mediated Semipinacol Rearrangement via C–X Bond Cleavage3 2-Iodoazolium-Salt-Catalyzed Reactions through Halogen Bonding (XB)3.1 TMSI-Co-catalyzed Dehydroxylative Coupling of Alcohols with ­Organosilanes3.2 Base-Co-catalyzed Umpolung Alkylation of Oxindoles with an ­Iodonium(III) Ylide3.3 Thiourea-Co-catalyzed N-Glycofunctionalization of Amides3.4 Thiourea-Co-catalyzed N-α-Glycosylation of Amides4 Catalytic Reactions Using 2-Haloazolium Salts as the Brønsted Acids4.1 N-β-Glycosylation of Amides4.2 N-β-2-Deoxyglycosylation of Amides5 Conclusions

Substituted Azolium Disposition: Examining the Effects of Alkyl Placement on Thermal Properties

We describe the thermal phase characteristics of a series of 4,5-bis(n-alkyl)azolium salts that were studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized-light optical microscopy (POM), and synchrotron-based small- to wide-angle X-ray scattering (SWAXS) measurements. Key results were obtained for 1,3-dimethyl-4,5-bis(n-undecyl)imidazolium iodide (1-11), 1,3-dimethyl-4,5-bis(n-pentadecyl)- imidazolium iodide (1-15), and 1,2,3-trimethyl-4,5-bis(n-pentadecyl)imidazolium iodide (2), which were found to adopt enantiotropic smectic A mesophases. Liquid-crystalline mesophases were not observed for 1,3-dimethyl-4,5-bis(n-heptyl)imidazolium iodide (1-7), 3-methyl-4,5-bis(n-penta-decyl)thiazolium iodide (3), and 2-amino-4,5-bis(n-pentadecyl)imidazolium chloride (4). Installing substituents in the 4- and 5-positions of the imidazolium salts appears to increase melting points while lowering clearing points when compared to data reported for 1,3-disubstituted analogues.

Correction: Alkoxy radicals generation: facile photocatalytic reduction of N-alkoxyazinium or azolium salts

Correction for ‘Alkoxy radicals generation: facile photocatalytic reduction of N-alkoxyazinium or azolium salts’ by Luca Capaldo et al., Chem. Commun., 2019, DOI: 10.1039/c9cc00035f.

Alkoxy radicals generation: facile photocatalytic reduction of N-alkoxyazinium or azolium salts

The photocatalytic reduction of N-alkoxyazinium or azolium salts allowed the facile generation of alkoxy radicals to be exploited in synthesis.