a-You Hu

Heck‐Type Cross‐Dehydrogenative Coupling Reactions of Indolizines at the 3‐Position with Electron‐Deficient Alkenes through Palladium‐Catalyzed CH Activation

Carbon–carbon bond formation reactions are one of the most important processes in chemistry because of their importance in key steps to build more complex molecules from simple precursors. Among these reactions, carbon–carbon (sp–sp) bond formation can be used for the construction of biaryls, which are important structural motifs in many organic molecules. For this reason, the development of new methods for the synthesis of biheteroaryl scaffolds remains an ongoing challenge for organic chemists. Inspired by the need for green and sustainable chemistry, synthetic chemists are seeking more efficient ways to construct C C bonds of heterocyclic compounds. A transition metal catalyzed cross-dehydrogenative coupling (CDC) reaction with two C H bonds might be a good choice, because installation of functional groups is unnecessary, thus making synthetic routes shorter and more efficient. Among them, Hecktype processes are practically important, because they use olefins as basic building blocks, and the preparation methods are always highly stereoselective. The indolizine skeleton is abundant in many natural products, such as erythrinan alkaloids, swainsonine, slaframine, crepidine, gephyrotoxine, cryptowoline, and myrmicarin. These natural products as well as their synthetic derivatives were found to exhibit a variety of biological activities, including antibacterial, phosphatase and aromatase inhibiting, antioxidant, antidepressant, and antitumor activities. They were also known to be calcium entry blockers and 5-hydroxytryptamine receptor antagonists. In addition, polycyclic indolizine derivatives were observed to have long-wavelength absorption and fluorescence in the visible-light region. Furthermore, the successful synthesis of these types of compounds has facilitated the development of novel classes of dyes and biological markers. Several groups have previously reported some palladiumcatalyzed C H activation reactions of indolizines at the 3position (Scheme 1). As a follow-up to our reported methods, we herein report a CDC reaction of indolizines with

Synthesis of pyrrolo[2,1,5-cd]indolizines through dehydrogenative Heck annelation of indolizines with diaryl acetylenes using dioxygen as an oxidant.

A dehydrogenative Heck annelation reaction of indolizine with diaryl acetylene via dual C-H bond cleavage was developed. Oxygen gas was employed as a clean oxidant in this catalysis under base-free conditions. Diarylpyrrolo[2,1,5-cd]indolizines were synthesized with high atom economy. In addition, kinetic isotope experiments provided evidence for C-H bond metalation of the 5-position of the indolizine as the rate-limiting step.

Copper acetate monohydrate: a cheap but efficient oxidant for synthesizing multi-substituted indolizines from pyridinium ylides and electron deficient alkenes

We report a highly practical one-pot method for synthesizing multi-substituted indolizines from α-halide carbonyl compounds, pyridines and electron deficient alkenes in the presence of copper acetate monohydrate and sodium acetate in DMF. A variety of function groups are tolerable in standard reaction conditions, including aldehyde. 36 examples were presented. The yield of indolizine was from moderate to high. Furthermore, multi-substituted indolizines can be prepared at gram scale by this method.

One-pot synthesis of indolizine via 1,3-dipolar cycloaddition using a sub-equivalent amount of K2Cr2O7 as an efficient oxidant under base free conditions

A one-pot method for synthesizing multi-substituted indolizines from α-halo-carbonyl compounds, pyridines and electron deficient alkenes was developed. A sub-equivalent amount of potassium dichromate was used as an oxidant under base free conditions. The transformation developed should be of economic efficiency.

Synthesis of Pyrrole via a Silver-Catalyzed 1,3-Dipolar Cycloaddition/Oxidative Dehydrogenative Aromatization Tandem Reaction

Pyrroles are an important group of heterocyclic compounds with a wide range of interesting properties, which have resulted in numerous applications in a variety of fields. Despite the importance of these compounds, there have been few reports in the literature pertaining to the synthesis of pyrroles from simple alkenes using a one-pot sequential 1,3-dipolar cycloaddition/aromatization reaction sequence. Herein, we report the development of a benzoyl peroxide-mediated oxidative dehydrogenative aromatization reaction for the construction of pyrroles. We subsequently developed a one-pot tandem reaction that combined this new method with a well-defined silver-catalyzed 1,3-dipolar cycloaddition reaction, thereby providing a practical method for the synthesis of multisubstituted pyrroles from easy available alkenes. The mechanism of this oxidative dehydrogenative aromatization reaction was also examined in detail.

Aza-Wacker-Type Reaction between Electron-Deficient Olefins and N-Alkylsulfonamides

A palladium-catalyzed oxidative amination protocol of electron-deficient olefins by aza-Wacker-type reaction with N-alkylsulfonamides was developed. The presence of the stoichiometric amount of methanesulfonic acid was crucial for the success of this transformation. The reactions were conducted in green solvent under mild conditions and scalable with excellent E-type stereoselectivity. In addition, a Pd(II)/Pd(0) catalytic cycle with the existence of a very strong oxidant (Selectfluor) was proposed.

Cd(II) and Cu(II) coordination polymers based on a multidentate N-donor ligand: syntheses, crystal structures, optical band gaps, and photoluminescence

Four Cd(II)- and Cu(II)-containing coordination polymers (CPs) based on a multidentate N-donor ligand and varied dicarboxylate anions, [Cd(3,3′-tmbpt)(p-bdc)]·2.5H2O (1), [Cd(3,3′-tmbpt)(m-bdc)]·2H2O (2), [Cu(3,3′-tmbpt)(m-bdc)]·H2O (3), and [Cu(3,3′-tmbpt)(p-bdc)]·2H2O (4), where 3,3′-tmbpt = 1 − ((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(3-pyridyl)-1,2,4-triazole, p-H2bdc = 1,4-benzenedicarboxylic acid, and m-H2bdc = 1,3-benzenedicarboxylic acid, have been prepared hydrothermally. The structures of the compounds were determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra and elemental analyses. Compound 1 exhibits a 3-D twofold interpenetrating framework with a 65·8 CdSO4 topology. Compound 2 is a 2-D layer containing meso-helical chains with a 44·62 sql topology. Compound 3 shows a 1-D → 3-D interdigitated architecture while 4 displays a 2-D → 3-D interdigitated architecture. The structural differences of the compounds indicate that the dicarboxylate anions and the central metal ions play important roles in the resulting structures of CPs. Optical band gaps and solid-state photoluminescent properties have also been studied. Graphical abstract