Synlett

Benzimidazole atropisomers bearing a C–N axis are privileged structural frameworks in pharmaceutical and natural products, thus appealing an increasing interest for its asymmetric synthesis. Here, we briefly discuss recent advances in the asymmetric synthesis of benzimidazole atropisomers with a C–N axis, with particular attention to our recently developed palladium-catalyzed intramolecular Buchwald–Hartwig amination strategy.

A CuCl-catalyzed hydrosilylation of allenes with PhSiH3 has been developed. It is the first example of using readily available cheap silane reagents to generate branched allylsilanes in copper-catalyzed allene hydrosilylation. This base-metal catalyst offered an atom-economical and efficient route to branched allylsilanes with excellent regioselectivity.

The synthesis of cyclopropyl pinacol boronic esters from dibromocyclopropanes via Matteson–Pasto rearrangement is reported. The method is readily scalable and shows limited levels of stereoinduction, with a selectivity that is in part complementary to that observed in existing stereoselective borylcyclopropanation strategies. The method can be used to rapidly access borylcyclopropanes as interesting building blocks for diversely functionalized cyclopropanes.

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.