Homotropylidene complexes

Access to alkyl substituted derivatives of the homotropylidene complexes is provided via the >j4-tropone iron complex by reaction with diazoalkanes, followed by mild thermolysis of the 3+2 py razoline adduct to give the corresponding homotropone complexes (equation 149)217,218. The 8,8-dimethyl derivative was used as starting material for the preparation of the fluxional ( 5-2,8,8-trimethylbicyclo[5.1.0]octa-2,4-dienylium)Fe(CO)3 cation complex219. More recently (homotropone)Fe(CO)3 was used for the synthesis of unique chiral 1,2-homoheptafulvene iron complexes220 221. 

For the synthesis of oxiranes with more complex structures, the peracid method is combined with other epoxidation procedures examples are the syntheses of ( )-crotoxirane, ( )-epicrotoxirane, and ( )-isocrotoxirane ° or the preparation of cis-trioxatris-(a)homotropylidene. o-Sulfoperbenzoic acid has been used for the stereoselective epoxidation of cholesterol. The selective epoxidation of cholest-5-en-3-one too has been examined. In the synthesis of 25-hydroxycholesterol selective epoxidation occurs on and 26 is formed. The epoxidation of olefin propellanes 27 and 28 can be achieved with MCPBA. As a consequence of the secondary orbital interaction, syn-attack is more marked in the case of 28. ° Epoxypropelladiene can be synthesized in accordance with Eq. 12. ... 

As we have noted several times in this chapter, just because a pericyclic reaction is allowed does not necessarily mean that it is facile. However, one particularly facile reaction is a [3,3] shift involving a (T bond that migrates from and to a cyclopropane ring. A prototypical example is the rearrangement of homotropylidene (shown in the margin). Even more complex examples of this kind of are known, and the most famous involves bullvalene, which is described in the next Going Deeper highlight. 

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