Synlett

Herein, we describe the synthesis of a wide variety of imines through oxidative coupling of alcohols and aromatic amines catalyzed by Mn complexes bearing N^N triazole ligands. A wide variety of imines in excellent yields (up to 99%) have been prepared. Mn-based catalysts proved to be highly efficient and versatile, allowing for the first time the preparation of several imines containing N-based heterocycles.

A divergent synthesis of isobenzofuran-1(3H)-one and 3,4-dihydroisochroman-1-one derivatives has been realized through the reaction of o-alkenyl benzoic acids/amides with PhICl2 and diphenyl disulfides/diselenides. Depending on the substitution type of the o-alkenyl benzoic acid or amide, this metal-free intramolecular oxychalcogenation approach regioselectively affords isobenzofuran-1(3H)-ones or 3,4-dihydroisochroman-1-ones through 5-exo-trig or 6-endo-trig cyclization processes, respectively.

Functionalized cyclic amines are essential structural motifs in synthetic chemistry and pharmaceutical chemistry, and Shono-type oxidation is a well-developed electrochemical approach for the synthesis of α- amines. In sharp contrast, electrochemically driven direct β-C(sp3)–H functionalization of amines has been far proven elusive. Herein, we outline the recent advances in this field and highlight our group’s effort to achieve electrochemical β-C(sp3)–H functionalization assisted by ferrocene as molecular electrocatalyst under mild conditions.1 Introduction2 Case studies of α-Functionalization (Shono-Type Oxidation)3 Electrochemical β-C(sp3)–H Acylation4 Conclusion

Ferrocenium-doped manganese(IV) oxide (Fc+/MnO2) was synthesized through accelerated decomposition of KMnO4 in the presence of ferrocenium ion (Fc+) generated by concentrated sulfuric acid. The corresponding catalysts enabled highly efficient oxidation of alcohols with aldehyde or ketone.

C
2-Symmetrical chiral amino alcohol ligands with a central thiophene moiety were shown to be effective in combination with CuCl2 for the asymmetric acylation of dl-hydrobenzoins. In contrast to previously developed chiral ligands, readily available acetyl chloride and acetic anhydride can be used as reagents, in addition to benzoyl chloride, giving rise to the corresponding monoacylated products in up to 99% ee (S = 532).

An expedient access to a series of nonsymmetrical bis(indolyl)methanes (BIMs) through transindolylation of readily available symmetrical 3,3′-BIMs with various indoles catalyzed by silica-supported sulfuric acid has been established. This approach not only provides a useful strategy for the synthesis of structurally diverse BIMs, but also provides examples of nucleophilic substitution of BIMs with aromatic and nonaromatic π-systems, leading to a library of indolyl-substituted tri- and diarylmethanes. Moreover, this method was successfully applied in the first total synthesis of the 2,3′-BIM alkaloid (±)-colletotryptin E in three steps with an overall yield of 46%. The features of this procedure include a metal-free process, an inexpensive and environmentally friendly catalyst, mild reaction conditions, broad functional-group tolerance, good yields, and gram-scalable preparations.

8-Aminoindolizidines were synthesized from l-asparagine as the chiral starting material. The key dibenzylamino succinimide intermediate was synthesized in two steps. Three homologs of chiral hydroxy lactams tethered with hydroxyalkenes were synthesized from the succinimide through a sequence involving N-alkylation, cross-olefin metathesis, and hydride reduction. The dibenzylamino group gave stereocontrol of the key N-acyliminium ion cyclization of these hydroxy lactams. 5-Substituted aminoindolizidines were synthesized with high diastereoselectivity at C6. A tandem cyclization of an N-(6-hydroxyhex-3-en-1-yl) γ-hydroxy lactam resulted in the formation of a tetrahydrofurano[2,3-g]indolizidine system.

Two diaryl derivatives of 1,1,4,4-tetracyanobuta-1,3-diene were synthesized for use as colorimetric ion sensors in aqueous media. The key synthetic step involved a [2+2]-cycloaddition/retro-cycloaddition between an electron-rich diarylethyne and electron-deficient tetracyanoethene. The compound bearing two sulfonamide groups showed good selectivity toward hydrogen sulfide ion, with a detection limit of 15.5 μM. The use of this sensor for the quantitative analysis of hydrogen sulfide ion in water samples was successfully demonstrated.

The synthesis and characterization of a novel class of pillar[4]arene[1]thioarenes (P[4]A[1]SMe) are reported. An oxidation–thionation strategy was used to replace a single dialkoxybenzene panel in the parent pillar[5]arene. 1H NMR spectroscopic titration experiments, supported by density functional theory computational studies, revealed that P[4]A[1]SMe show starkly modulated host–guest binding properties for electron-deficient aliphatic guests.

A novel method has been developed for the synthesis of 1,5-disubstituted tetrazoles from nitrones by using bis(p-nitrophenyl) phosphorazidate in the presence of 4-(dimethylamino)pyridine. By this approach, various nitrones were converted into the corresponding tetrazoles. This method permits the preparation of 1,5-disubstituted tetrazoles without the need for toxic or explosive reagents.