Borepin is a seven-membered unsaturated ring system containing a tricoordinate boron. Although many borepin compounds annulated with aromatic systems have been reported to date, only one [b,d,f]-annulated tetracyclic borepins has been synthesized. In the present study, we synthesized benzo[d]-dithieno[b,f]borepins as a new class of building blocks for functional materials motivated by the following structural features: (1) the high chemical stability of dithieno[b,f]borepin species; (2) the highly conjugated tetracyclic system with a borepin ring; and (3) electronic structures that are easily tuned by the introduction of functional groups on the annulated benzene ring. The prepared borepins were stable in air both in solution and as solids, and the electronic states could be finely tuned by changing the substituents on the benzene ring. Interestingly, DFT calculations revealed that the LUMO and LUMO+1 energy levels were strongly affected by the benzo[d]-annulation, depending on the boron-bridged positions on the fused thiophene rings. NICS and HOMA methods proved that the aromaticity of the borepin ring in the benzo[d]dithieno[b,f]borepin system is relatively small. We also report an unexpected red emission observed for the first time in borepin compounds for benzo[d]dithieno[b,f]borepin in the solid state.

The enantioselective synthesis of the diterpenic moiety in the abeo-breviano skeleton is reported. The synthesis is carried out starting from 2-methyl-1,3-cyclohexanedione and EVK in eleven steps following a ring-expansion strategy once the tricyclic perhydrophenantrene skeleton has been obtained. A new Tiffeneau-Demjanov rearrangement under dark conditions is reported in which the insertion of the new methylene group is directed towards the most hindered side of the carbonyl group. This result is new and opposite to those reported in the literature under light (filtered or un-filtered wavelengths) conditions where insertion in the less hindered side is usually preferred. (C) 2010 Elsevier Ltd. All rights reserved.

Hydrogen, fluorine and chlorine addition reactions with C(36)(D(6h)) have been investigated by the density function theory method at B3LYP/6-31 G(d) level. The interaction potential between C(36)(D(6h)) and atom X (X = H and F) shows that there are three possible isomers of C(36)X (X = H and F). The structures and energies order of the possible stable isomers of C(36)X are discussed. In addition, the transition states, as well as reaction pathway of X transfer reactions between different key points are given to explore the possible reaction mechanism. Finally, the stability of C(36)X(2) is discussed through the density functional theory.

The practical asymmetric synthesis of amathaspiramides B, D, and F has been accomplished by utilizing an aza-Barbier allylation as the key step to construct the common intermediate with two adjacent stereocenters. A kinetically controlled cyclization to build the challenging thermodynamically less stable 8R-hemiaminal moiety is also important in the synthesis of amathaspiramide D. The route is readily scalable, and gram quantity of the final product D has been prepared.