Palladium-catalyzed diarylmethyl C(sp3)-C(sp2) bond formation: a new coupling approach toward triarylmethanes

Palladium-catalyzed reductive coupling reactions between N-tosylhydrazones and aryl halides lead to the formation of C(sp(3))-C(sp(2)) bonds. This approach provides a general route for the synthesis of triarylmethanes.

Subtle electronic effects in metal-free rearrangement of allenic alcohols

A general and stereoselective rearrangement of allenic alcohols to (E,E)-1,3-dien-2-yl triflates and chlorides was developed under metal-free conditions. Subtle electronic effects of the alkyl and aryl substituents on the carbon bearing the hydroxyl group has a profound impact on the reaction rate and efficiency such that vinyl triflates were obtained from electron-deficient substrates and trimethylsilyl triflate whereas vinyl chlorides were generated with an electron-rich substrate and trimethylsilyl chloride.

Diazo compounds and N-tosylhydrazones: novel cross-coupling partners in transition-metal-catalyzed reactions

Transition-metal-catalyzed carbene transformations and cross-couplings represent two major reaction types in organometallic chemistry and organic synthesis. However, for a long period of time, these two important areas have evolved separately, with essentially no overlap or integration. Thus, an intriguing question has emerged: can cross-coupling and metal carbene transformations be merged into a single reaction cycle? Such a combination could facilitate the development of novel carbon-carbon bond-forming methodologies. Although this concept was first explored about 10 years ago, rapid developments inthis area have been achieved recently. Palladium catalysts can be used to couple diazo compounds with a wide variety of organic halides. Under oxidative coupling conditions, diazo compounds can also react with arylboronic acids and terminal alkynes. Both of these coupling reactions form carbon-carbon double bonds. As the key step in these catalytic processes, Pd carbene migratory insertion plays a vital role in merging the elementary steps of Pd intermediates, leading to novel carbon-carbon bond formations. Because the diazo substrates can be generated in situ from N-tosylhydrazones in the presence of base, the N-tosylhydrazones can be used as reaction partners, making this type of cross-coupling reaction practical in organic synthesis. N-Tosylhydrazones are easily derived from the corresponding aldehydes or ketones. The Pd-catalyzed cross-coupling of N-tosylhydrazones is considered a complementary reaction to the classic Shapiro reaction for converting carbonyl functionalities into carbon-carbon double bonds. It can also serve as an alternative approach for the Pd-catalyzed cross-coupling of carbonyl compounds, which is usually achieved via triflates. The combination of carbene formation and cross-coupling in a single catalytic cycle is not limited to Pd-catalyzed reactions. Recent studies of Cu-, Rh-, Ni-, and Co-catalyzed cross-coupling reactions with diazo compounds or N-tosylhydrazones show that these transformations also work with other transition metals, demonstrating the generality of the diazo compounds as new cross-coupling partners in transition-metal-catalyzed coupling reactions.

An easy access to fluoroalkanes by deoxygenative hydrofluorination of carbonyl compounds via their tosylhydrazones

An efficient and operationally simple synthesis of fluoroalkanes by deoxygenative hydrofluorination of carbonyl compounds via their tosylhydrazone surrogates is reported. The reaction can be carried out in a one-pot procedure directly from carbonyl compounds.

Bifunctionalisation of 1,4-naphthoquinone by the Oxidative Addition of an Alkylamine and Iodine

Novel 2-iodo-3-(alkylamino) naphthalene-1,4-diones are formed in 33–70% yield by the reaction of alkylamine and 1, 4-naphthoquinone in the presence of iodine.

Synthesis, biological evaluation, and structure-activity relationships of tri- and tetrasubstituted olefins related to isocombretastatin A-4 as new tubulin inhibitors

The synthesis and structure-activity relationships associated with a series of 1,1-diarylethylene tubulin polymerization inhibitors 3 and 4 are described. The key step for their preparation involves a palladium-catalyzed coupling of N-arylsulfonylhydrazones with aryl halides, thus providing flexible and convergent access to tri- and tetrasubstituted 1,1-diarylolefins 3 and 4 related to isocombretastatin A-4 (isoCA-4). These compounds have been evaluated for tubulin polymerization inhibitory activity as well as for cytotoxic activity. The most potent compounds are 1,1-diaryl-2-methoxyethylenes 4b, 4d and 4e having a trisubstituted double bond. They exhibited good antiproliferative activity against various human cancer cell lines (GI(50) = 8-80 nM). Compounds 4b and 4e strongly inhibited tubulin polymerization with IC(50) values of 2 and 3 μM, respectively, and induced cell cycle arrest in the G(2)/M phase in the K562 cell line. Docking studies in the colchicine binding site of tubulin allowed identification of residues most likely to interact with these inhibitors and explain their potent anti-tubulin activity.

Rhodium-catalyzed oxidative annulation of sulfonylhydrazones with alkenes

An efficient rhodium-catalyzed tandem C-H bond olefination and annulation approach was developed to afford 1,2-dihydrophthalazines in good to excellent yields from easily accessible sulfonylhydrazones and alkenes.