Synlett

A mild and convenient method for the synthesis of 2,2-dihaloketones and gem-dihalolactols has been developed. For the synthesis of 2,2-dihaloketones, alkynes were employed as substrates to react with halogenating agents, Cl2 or ClBr, that were generated in situ from aqueous HCl and NCS or NBS, respectively. On the other hand, gem-dihalolactols could be prepared from alkynol substrates by using the same reaction conditions. This method could be applied to a broad range of substrates to give the corresponding products in low to good yields.

Unsymmetrical 1,1,2-triacylalkenes were conveniently prepared by the oxidative coupling of 1,3-keto esters with terminal alkynes by employing 4.0 equivalents of inexpensive ceric ammonium nitrate (CAN) as the oxidant in acetonitrile as the solvent at 0 °C. The method is milder than previously reported methods and can be conducted under air, thereby demonstrating its practicality and versatility for preparing these useful building blocks. The reaction is believed to occur by a single-electron-transfer process of the 1,3-keto ester substrate initiated by CAN to generate an α-radical species that quickly adds to the terminal alkyne partner in the reaction. Subsequent oxidation of the resulting vinyl radical by air and CAN then leads to the formation of the triacylalkene product as a mixture of E- and Z-isomers. The reaction was shown to be general, with 27 illustrative examples of the formation of the desired products in up to quantitative yield and with moderate to excellent alkene geometrical selectivities.

New solution-processable chrysene-basked deep-blue fluorescent dendrimers consisting of chrysene as a core end-capped by carbazole dendrons were designed, synthesized, and characterized. These dendrimers exhibit strong deep-blue emissions in solution or thin-film states with decent hole mobility and high thermal and electrochemical stability. They can be effectively used as nondoped emitters in organic light-emitting diodes (OLEDs). The nondoped OLEDs, which have a simple structure, showed good electroluminescence (EL) performance (luminance: 2334–2400 cd m–2; external quantum efficiency: 1.88-2.51%; turn-on voltage: 3.8–4.0 V) and deep-blue EL spectra (CIE y: 0.065–0.075) with a narrow full width at half maximum of 61–65 nm.

The palladium(II)-catalyzed carbonylation of alkenes presents one of most efficient methods for the synthesis of alkyl-substituted carbonyls and has received much attention. In this Account, we summarize our recent studies on the palladium-catalyzed intermolecular carbonylation-based 1,2-difunctionalization of alkenes, in which two strategies were involved: (1) a cooperative strategy involves the sequential iodine(III)-mediated alkene activation and palladium-catalyzed carbonylation, leading to the intermolecular β-oxy-, fluoro-, and azidocarbonylation of alkenes; (2) the classic strategy initiated by intermolecular nucleopalladation and carbonylation, including the asymmetric oxycarbonylation of alkenes. These methods provide a series of efficient approaches to synthesize β-functionalized aliphatic carboxylic derivatives.1 Introduction2 A Cooperative Strategy Involving Iodine(III)-Mediated Alkene Activation and Palladium-Catalyzed Carbonylation2.1 Intermolecular Oxycarbonylation of Alkenes2.2 Intermolecular Fluorocarbonylation of Alkenes2.3 Intermolecular Azidocarbonylation of Alkenes3 Intermolecular Aminocarbonylation of Alkenes Initiated by Aminopalladation4 Intermolecular Arylcarbonylation of Alkenes Initiated by Arylpalladation5 Intermolecular Enantioselective Oxycarbonylation of Alkenes Initiated by Oxypalladation6 Conclusion

Heteroarenes are important units in organic chemistry and are ubiquitous in natural products, pharmaceuticals, and numerous artificial molecules. Despite great efforts devoted to accessing heteroarenes, the development of new methods to efficiently produce heteroarenes remains a long-term interest. Recently, the strategy of radical-mediated heteroaryl migration has supplied a robust toolkit for the synthesis of a diversity of heteroaryl-containing compounds. This Account summarizes our recent achievements in this field and provides insight into the incorporation of heteroarenes into organic skeletons.1 Introduction2 Radical-Mediated Heteroarylation of Alkanes and Alkenes via Intramolecular Heteroaryl Migration2.1 C(sp3)–H Heteroarylation via Intramolecular Heteroaryl Migration2.2 Difunctionalization of Alkenes via Intramolecular Heteroaryl Migration3 Intermolecular Difunctionalization of Alkenes via ‘Docking-Migration’ Strategy3.1 Sulfone-Based Bifunctional Reagents for Difunctionalization of Alkenes by Docking Migration3.2 Sulfone-Based Reagents for the Synthesis of N-Fused Heteroarenes by Docking Migration3.3 Tertiary Alcohol Based Bifunctional Reagents for Difunctionalization of Alkenes by Docking Migration3.4 Diaryl Ether Based Bifunctional Reagents for Difunctionalization of Alkenes by Docking Migration3.5 Conclusion

Here we report a microfluidic system for photochemical cycloadditions fabricated using silicon micro processing technologies. The system was optimized to yield residence times of just a few minutes for a range of photochemical [2+2]-cycloaddition reactions facilitated using high power UV-LEDs at 375 nm and triplet photosensitizers, which removed the need for the low wavelengths typically required for these types of transformations. Adducts using different excitable olefins with different linear, carbocyclic, and heterocyclic coupling partners were explored to demonstrate the feasibility of performing photochemistry in microflow in an academic research environment. Finally, a reaction leading to a novel dihydrooxepin-2(3H)-one scaffold and a mechanistic proposal for its formation are reported.

A direct access to O-heterocycles by Bi(OTf)3-catalyzed intermolecular cyclization of phenols with diols is described. Catalytic dehydrative tandem formation of C–O and C–C bonds was achieved by using a Bi(OTf)3 catalyst without any additives. The catalytic intermolecular cyclization of phenols with various diols proceeded to give the corresponding chromanes in up to 91% yield and/or pyran derivatives in up to 66% yield.

A facile approach for the synthesis of benzimidazolones via a Ph3P–I2 promoted reaction of hydroxamic acids is reported. Upon Lossen-type rearrangement of the O-activated hydroxamic acids, the in situ generated isocyanates undergo an intramolecular attack by ortho N-nucleophiles producing the cyclized products in good yields under mild conditions. The method allows the direct preparation of a single regioisomer of N-monosubstituted derivatives using readily accessible starting materials and low-cost reagents with broad substrate scope.

A facile and efficient method has been developed for the synthesis of fluorenes by Pd-catalyzed C–H alkylation of biphenyl-2-yl trifluoromethanesulfonates. The trifluoromethanesulfonates are more readily available and more environmentally benign than biphenyl iodides, and are advantageous substrates for traceless directing-group-assisted C–H activation. The reaction generates C,C-palladacycles as the key intermediates that form two C(sp2)–C(sp3) bonds through reaction with CH2Br2. The reaction tolerates various functional groups, permitting easy access to a range of fluorene derivatives.

Carbohydrates have played an important role in organic synthesis. Since they contain many stereocenters, they have been widely used as chiral-pool starting materials. Herein, we report the asymmetric formal synthesis of (–)-swainsonine, which exhibits anticancer and immunosuppressive activities and inhibits lysosomal α-mannosidase activity, from d-mannose and d-arabinose. The synthesis utilized Zn-mediated Bernet–Vasella reaction, Horner–Wadsworth–Emmons olefination, and Grubbs olefin metathesis as key reactions.