The double [3+2] photocycloaddition reaction

One of a synthetic organic chemists‟ greatest challenges is to create step-efficient routes toward compounds with high molecular complexity. Therefore, reactions such as the meta photocycloaddition of an olefin to a benzene derivative, which provide more than one bond in a single step are of significant importance. It this remarkable reaction three new σ bonds, three new rings and up to six new stereocenters are formed simultaneously. Additional complexity can be added by tethering the two reacting partners together and this form of the reaction has found many uses in natural product synthesis. In this work a remarkable double [3+2] photocycloaddition reaction is reported that results in the formation of a complex cis, cis, cis, trans-[5, 5, 5, 5] fenestrane derivative from a simple flat aromatic acetal with two branching alkenes. During this dramatic transformation four carboncarbon bonds, five new rings and seven new stereocenters are created in a single one-pot process using only UV light. The reaction occurs in a sequential manner from the linear meta photocycloadduct, via a secondary [3+2] addition of the alkene across the cyclopropane of the adduct. In addition, an angular meta photocycloadduct also produced in the initial addition step, undergoes an alternative fragmentation-translocation photoreaction to afford a silphinene-like angular tricyclic compound. In this work the investigation of this newly discovered process is discussed via the synthesis and subsequent irradiation of a series of photosubstrates containing different functional groups in the arene-alkene tether. In addition, attempts toward the synthesis of alternative structures using the same double [3+2] photocycloaddition are reported

Radical reductions of alkyl halides bearing electron withdrawing groups with N-heterocyclic carbene boranes

1,3-Dimethylimidazol-2-ylidene borane and 2,4-dimethyl-1,2,4-triazol-3- ylidene borane are found to be useful reagents for the reduction of alkyl iodides and bromides bearing nearby electron withdrawing substituents. Signatures of radical chain reactions are seen in many cases, but ionic reductions may also be occurring with some substrates. The reagents are attractive because of their low molecular weight, their availability from inexpensive precursors, and their stability. Separation of the borane products from the target products is readily accomplished either with or without prior regeneration of the borane for later reuse. 2,4-Dimethyl-1,2,4-triazol-3-ylidene borane is versatile because both starting borane and its derived products can be removed by extraction with water. © 2011 The Royal Society of Chemistry

Synthesis of Triangular Tripalladium Cations as Noble-Metal Analogues of the Cyclopropenyl Cation

The first C-3-symmetric 44-core-valence-electron triangular palladium clusters, [{(SAr)(PAr3)Pd}(3)](+), have been synthesized by activation of the CS bond of isothioureas. Owing to delocalized metal-metal bonding, these stable complexes are the first noble-metal analogues of the -aromatic cyclopropenyl cation [C3H3](+), with their all-metal aromaticity involving d-type atomic orbital

NHC-catalyzed chemo- and regioselective hydrosilylation of carbonyl derivatives

The hydrosilylation of carbonyl derivatives has been explored by the activation of diphenylsilane in the presence of a catalytic amount of an N-heterocyclic carbene (NHC). Presumably, a hypervalent silicon intermediate featuring strong Lewis acid character allows dual activation of both the carbonyl moiety and the hydride at the silicon center. Reduction under mild conditions could be accomplished using this organocatalytic process. Some interesting selectivities have been encountered. © Georg Thieme Verlag Stuttgart · New York

The Cyanamide Moiety, Synthesis and Reactivity

The cyanamide moiety provides many opportunities as a building block for the synthesis of nitrogen-containing heterocycles. This review discusses the reported methods for the preparation of alkyl- and N-acylcyanamides and illustrates their reactivity vis-à-vis nucleophilic additions, cycloadditions, radical chemistry and coordination chemistr