G. B. M. Kostermans

7,8-dimethoxycarbonyl-10,11-dimethyl[5]paracyclophane

Abstract The title compound ( 1 ) was obtained in 13% yield by UV irradiation of the corresponding Dewar benzene ( 2 ); it is considerably more stable than [5]paracyclophane itself.

Photochemical synthesis of arenetricarbonylchromium(0) complexes: scope and limitations

Abstract Two photochemical methods for the preparation of arenetricarbonylchromium(0) complexes are described. The first involves irradiation of a solution of hexacarbonylchromium(0) and arene in THF at room temperature with a medium pressure mercury lamp. In the second a suspension of hexacarbonylchromium(0) in THF is irradiated in the same way and the arene then added. The yields are generally lower than those obtained by the usual thermal methods, but there is advantage in the milder reactions conditions.

The synthesis of hetero-bridged [5](3,6)oxepinophanes

The [5](3,6)oxepinophanes (8) are the oxepines with the shortest bridge reported so far. They were obtained starting from diethyl furan-3,4-dicarboxylate (3) which, with lithium aluminium hydride, afforded the diol (4); this was converted into the seven-membered siloxanes (5a and b) by reaction with dichlorodimethylsilane or dichlorodimesitylsilane, respectively. By the Prinzbach–Tochtermann sequence, compounds (5) were converted into the oxepinophanes (8) in three steps: Diels–Alder reaction of (5) with dimethyl acetylenedicarboxylate to give the fused 7-oxanobornadienes (6), photochemical transformations of compounds (6) to the fused 7-oxaquadricyclanes (7), and thermal isomerization of compounds (7) to (8). Attempted conversion of (8a) into (11a), a derivative of [5]paracyclophane, was unsuccessful.

Small [N]Cyclophanes. Where is the Limit?

Dewar benzenes 1 and 3 are appropriate precursors of small [n] cyclophanes(n<8): in fact the complete skeleton of the cyclophane is present and the high energy content of the Dewar benzene system is available to compensate for any strain and instability in 2 or 4 which might tend to jeopardize the transformation.