A photochemical study of dibenzobarrelene amides and ester-amides: solution and solid state rearrangements

The photochemical reactions of various dibenzobarrelene acyl derivatives has been investigated in solution and in the solid state. These derivatives consisted of monoamides, symmetrical diamides, mixed ester-amides, and mixed ester-thioesters. The two types of reactions found in the irradiation of these systems were the di-π-methane rearrangement and/or hydrogen abstraction. Photolysis of dibenzobarrelene monoamides in solution and in the solid state gave a symmetrical dibenzosemibullvalene photoproduct. Two monoamides (R,R = Bz and R,R = iPr) gave ring-fused spiro β-lactam analogues of the starting materials in addition to the semibullvalene product. These two amides also gave an ethano-bridged monosubstituted amide photoproduct as did a third monoamide (R,R = Et). Photolysis of all monoamides in the solid state resulted in the formation of semibullvalenes only. X-ray crystallographic analysis of the diethyl and the di-iso-propyl starting materials were performed in order to correlate the lack of hydrogen abstraction in solid state irradiations with the geometric constraints of the crystalline starting material. An X-ray crystallographic analysis of the dibenzyl amide-derived β lactam was also performed in order to establish the relationships between the various stereochemical centres in the molecule. A series of symmetrical diamides was prepared and photolyzed in solution and in the solid state. All diamides gave a single semibullvalene photoproduct upon irradiation in solution. Two of the starting materials (N,N-dimethyl and N,N-diethyl) also reacted rapidly and efficiently in the solid state to give the semibullvalene product, whereas two others (N-methyl and N-ethyl) were found to be very unreactive in the solid state. [more abstract]Science, Faculty ofChemistry, Department ofGraduat