Hexamethylbicyclo 2.2.0 hexadiene

In 15-58, we used the principle of conservation of orbital symmetry to explain why certain reactions take place readily and others do not. The orbital symmetry principle can also explain why certain molecules are stable though highly strained. For example, quadricyclane and hexamethylprismane are thermodynamically much less stable (because much more strained) than their corresponding isomeric dienes, norbomadiene and hexamethylbicyclo[2.2.0]hexadiene (108). Yet the... 

Reaction of ozone with a double bond is not surprisingly a function of the nucleophilicity or electron density of the double bond. Therefore, in ozonolysis of octamethylsemibullvalene (122) as well as for hexamethylbicyclo[2.2.0]-2,5-hexadiene and octamethyltricyclo-octadiene the diozonides, e.g. 123, are formed as the major product (equation 33). On the other hand, for hexachlorobicyclopentadiene (124), hexachlorobicycloheptadiene and 2-chloro-3-methyl-l,3-butadiene2i attack takes place at the nonchlorinated double bond only to form the ozonide 125 (equation 34). 

Previous reports have based the synthesis on the reaction of hexamethylbicyclo[2.2.0] hexadiene with Rh(III)CI].3H20. It has been suggested that pentamethylcyclopentadiene, which was not then commercially available, was the actual reactant in the hexa-methylbicyclo[2.2.0]hexadiene synthesis see B. L. Booth, R. N. Haszeldine, and M. Hill, J. Chem. Soc. (A), 1969, 1299 and P. M. Maitlis, Chem. Soc. Rev., 10, 1 (1981). 

Hexamethylbicyclo[2.2.0]hexadiene may be purchased from Columbia Organic Chemicals, Columbia, South Carolina, or Henley Chemical Company, New York, New York. The cost at the time of submission was approximately 150 per 200 g. 

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