Claas H. Hövelmann

Direct synthesis of bicyclic guanidines through unprecedented palladium(ii) catalysed diamination with copper chloride as oxidant.

Palladium catalysed intramolecular guanidine transfer to alkenes can be accomplished with copper chloride as the oxidant to give bicyclic guanidines with complete selectivity and in high yields.

Intramolecular Diamination of Alkenes with Palladium(II)/Copper(II) Bromide and IPy2BF4: The Role of Halogenated Intermediates

The oxidative intramolecular diamination of alkenes with tethered ureas and related groups as the nitrogen source has been investigated both with the iodonium reagent IPy(2)BF(4) (Py=pyridine) and under palladium catalysis in the presence of copper(II) bromide as a reoxidant. For terminal alkenes, the two procedures enable selective and high-yielding transformations. Studies with deuterated material led to the conclusion that the reactions proceed through different stereochemical pathways. An advanced protocol for palladium-catalyzed diamination through six-membered-ring annulation was also developed, and the first examples of the intramolecular diamination of internal alkenes are described. In this case, the same stereochemical outcome was observed for the iodonium-promoted and palladium-catalyzed transformations. On this basis, it was possible to determine the importance of aminohalogenated intermediates in both diamination reactions. Overall, the disclosed procedures broaden significantly the synthetic applicability of the oxidative intramolecular diamination of alkenes.

Synthesis of Diamino Carboxylic Esters by Palladium‐Catalyzed Oxidative Intramolecular Diamination of Acrylates

Unligated palladium(II) salts catalyze the oxidative diamination of acrylic esters to yield 2,3-diamino carboxylic esters. The reaction employs copper(II) bromide as oxidant and proceeds with good to excellent stereoselectivities and complete chemoselectivity. Preliminary mechanistic studies provide evidence for the involvement of a direct amination of the C--Pd bond in the alpha position relative to the ester group. This protocol significantly broadens the overall scope of the palladium-catalyzed diamination of alkenes and represents the first direct diamination of functionalized nonterminal substrates. The reaction yields readily protected 2,3-diamino acid derivatives, which can be considered as highly functionalized building blocks for subsequent synthesis. The use of one of these new diamination products as a suitable starting material in a short synthesis of the alkaloid absouline is demonstrated as an example.

Metal-free diamination of alkenes employing bromide catalysis

A unique metal-free intramolecular diamination of alkenes based on bromide catalysis is reported that uses only potassium bromide and sodium chlorite avoiding any use of transition metal. This unprecedented halide catalysis is of general applicability, uses economic reagents, can be conveniently up-scaled and proceeds under mild and selective conditions that surpass all conventional transition metals in scope.

First palladium- and nickel-catalyzed oxidative diamination of alkenes: Cyclic urea, sulfamide, and guanidine building blocks*

We recently reported the first catalytic diamination of alkenes. This protocol calls for the use of Pd(II) as catalyst in combination with PhI(OAc)2 as terminal oxidant and furnishes the final diamines as cyclic ureas. It consists of an unprecedented two-step reaction of aminopalladation and Csp3-N-bond formation involving a Pd(IV) species. Introduction of Ni(II) catalysts for homogeneous oxidation allows for an efficient diamination with sulfamides, which lead to convenient liberation of the free diamines. In related protocols, the substrate scope of the diamination has been broadened to the formation of cyclic guanidines.

Oxy-Functionalization of Nucleophilic Rhenium(I) Metal Carbon Bonds Catalyzed by Selenium(IV)

We report that SeO2 catalyzes the facile oxy-functionalization of (CO)5Re(I)-Me(delta-) with IO4(-) to generate methanol. Mechanistic studies and DFT calculations reveal that catalysis involves methyl group transfer from Re to the electrophilic Se center followed by oxidation and subsequent reductive functionalization of the resulting CH3Se(VI) species. Furthermore, (CO)3Re(I)(Bpy)-R (R = ethyl, n-propyl, and aryl) complexes show analogous transfer to SeO2 to generate the primary alcohols. This represents a new strategy for the oxy-functionalization of M-R(delta-) polarized bonds.

CCDC 866364: Experimental Crystal Structure Determination

Related Article: Patricia Chavez, Jonathan Kirsch, Claas H. Hovelmann, Jan Streuff, Marta Martinez-Belmonte, Eduardo C. Escudero-Adan, Eddy Martina and Kilian Muniz|2012|Chemical Science|3|2375|doi:10.1039/C2SC20242E