Multidirectional cobalt-catalyzed Diels-Alder/1,4-hydrovinylation sequences.

The combination of two powerful cobalt-catalyzed carbon-carbon bond forming transformations, namely, the Diels-Alder and the 1,4-hydrovinylation reaction, in a tandem or a sequential one-pot procedure, opened up a concise and efficient route to polysubstituted aromatic systems and cyclohex-3-enone derivatives. Furthermore, ozonolysis of the latter products led to polycarbonyl compounds with tailored carbonyl group distances which could be characterized via their respective BF(2)-borinane complexes. The cobalt catalysts tolerated several functional groups, and a flexible approach to polyfunctionalized compounds in concise fashion was described.

Cobalt- versus ruthenium-catalyzed Alder-ene reaction for the synthesis of credneramide A and B.

The first synthesis of the natural products credneramide A and B was accomplished by utilizing Alder-ene reactions between a terminal alkene and an internal alkyne to generate the rather uncommon 1,4-diene substructure of these compounds. Moreover, two different short linear sequences toward these targets are evaluated using either a cobalt-catalyzed Alder-ene reaction of 1-chloropent-1-yne or a ruthenium-catalyzed Alder-ene reaction of 1-trimethylsilyl-1-pentyne with 5-hexenoic acid derivatives in the key step transformation. In addition, saponification of the primary Alder-ene product derived from the cobalt-catalyzed Alder-ene reaction led to credneric acid, the biological precursor of both natural products.

Double- and triple-cobalt catalysis in multicomponent reactions.

The combination of different types of cobalt-catalyzed transformations in one-pot procedures is described. One of the key building blocks, a boron-functionalized isoprene derivative (boroprene), led to the realization of four-component reaction sequences comprising the cobalt-catalyzed Diels-Alder and a 1,4-hydrovinylation reaction. Eventually, a reaction sequence including a cobalt-catalyzed Diels-Alder reaction, a cobalt-catalyzed 1,4-hydrovinylation, an allylboration, and a cobalt-catalyzed Alder-ene reaction led to a five-component one-pot reaction sequence in which five carbon-carbon bonds were formed in excellent regio- and diastereoselectivity to generate complex products in good overall yields.

Multi-component regio- and diastereoselective cobalt-catalyzed hydrovinylation/allylboration reaction sequence.

The combination of a regioselective cobalt-catalyzed 1,4-hydrovinylation and the diastereoselective allylboronation reaction leads to a wide scope of functionalized hydroxydienyl esters in a one-pot reaction in excellent yields. With catalytic amounts of base, these products are easily converted either into α,β,γ,δ-unsaturated hydroxyl esters or complex tetrasubstituted tetrahydropyrans in chemo- and diastereoselective fashions. In addition, a high-yielding four-component one-pot reaction involving an acrylate, two different and unsymmetrical 1,3-dienes, and an unsaturated aldehyde is presented.

Regioselective cobalt-catalyzed alder-ene reaction toward silicon- and boron-functionalized building blocks.

The cobalt-catalyzed formal Alder-ene reaction of functionalized alkenes and alkynes leads to bifunctionalized 1,4-dienes in high yields and excellent regio- and stereoselectivities. The silicon-functionalized building blocks are easily converted into iodo-functionalized derivatives and in combination with boron-functionalized building blocks polyenes can be generated utilizing a Suzuki cross-coupling. In addition, building blocks incorporating allylic silane functionalities can be used in Sakurai allylation or Prins-type cyclization reactions for the synthesis of heterocyclic products such as tetrahydrofuranes or tetrahydropyranes.

Transparent silver microcrystals: synthesis and application for nanoscale analysis.

Micrometer-sized atomically flat silver nanoplates with a thickness of 10-20 nm were obtained in a one-pot reduction of silver nitrate with hydrazine sulfate without surfactants or polymers. The optically transparent triangles and hexagons have been proven to be excellent substrates for experiments with a tip-enhanced Raman transmission setup.