Low temperature x-ray diffraction analysis of 4,5,10,11-tetramethyl-heptacyclo[8.2.1.1(2,5).1(4,7).1(8,11).0(1,8).0(2,7)]hexadecane: DSC, MM2 and H-1 NMR study of its [2+2]retrocycloaddition to an isomeric diene

The synthesis of pure 3 has been achieved by deiodination of 1 with Na-K alloy at r.t. and by [2+2] photocyclization of diene 4. X-ray diffraction analysis at -30 degrees C of the thermally unstable 3 shows the cyclobutane ring to be highly rectangular with large central and short lateral bonds. Also, the C4-C5 and C10-C11 bonds in 3 and diene 4 are very large. A clear neat DSC conversion of 3 to 4 allowed us to obtain the Delta H and the Ea values for this transformation. Delta H is in good agreement with MM2 calculations, while Ea compares well with kinetic measurements in CDCl3 solution. Copyright (C) 1996 Elsevier Science Ltd