Science of Synthesis

Koo, S., Science of Synthesis, (2010) 45, 1402.

Cycloheptatrienes are a unique subclass of the conjugated polyenes, in which the polyenes are confined to a seven-membered ring structure. The cyclotautomerization process is an interesting property of these compounds.[‌168‌] The valence isomerization of cycloheptatriene (‌6‌) and norcaradiene (‌183‌) can be deduced by the identification of the reaction products (‌Scheme 40‌).[‌169‌] The 1H NMR spectroscopic characteristics (the chemical shift of HA) are also very informative as to the position of the equilibrium.[‌170‌] While the cycloheptatriene is generally the more stable tautomer, there are systems in which the norcaradiene form is preferred.[‌171‌,‌172‌] Cycloheptatrienes readily react with hydride abstractors, e.g. the triphenylcarbenium cation, to generate the aromatic tropylium cation ‌184‌.[‌173‌] The tropylium cation ‌184‌ reacts with diverse nucleophiles to give addition products. This addition reaction is an important method for the preparation of substituted cycloheptatrienes. Cycloheptatrienes have been traditionally prepared by thermal ring-expansion reaction, which often produces inseparable mixtures of isomers. Highly stereo- and regiocontrolled synthesis of cycloheptatrienes is possible by virtue of more recent progress in the transition-metal-mediated reactions. All of these preparation methods will be described in the following sections.

‌Meeeee 88‌ Meeeeee Meeeeeeeeeeee eee Meeeeeeeeeeee ee Meeeeeeeeeeeeeee

Meeeeeeeeeeeeeeee eeee eeee ee eeee eeeeeeeeeeeee eeeeee eeeeeeeeeeeeeee. Mee eeeeeeeeee eeeeeeee eeeeeeeeeee ee eeeeeee [8 + 8]-, [8 + 8]-, [8 + 8]-, eee [8 +8]-eeeeeeeeeeeee eeeeeeeee ee eeeee ee eeeeeee eeeeeeeeee eeeeeeeee.[‌888‌–‌888‌] Meeeeeeeeeeeeeeee eee ee eeeeee eeeeeeee ee eeeeee eeeeeeee ee eeeeeeeeeeeee,[‌888‌,‌888‌] eee eeeeeee ee eeeeeeeeeeeeeeee.[‌888‌] Meee eeeee eeeeeeeee ee eeeeeeeeeeeeeeeee eeee ee eeeeeeeeeeeee ee eeeeeeeee eee eeeeeeeeeeeeee ee eeeeeeeeeee eeeeeeee eeee eeee eeeeeeee.[‌888‌,‌888‌] Mee eeeee ee eeee eeeeeee ee eeeeeee ee eee eeeeeeeee ee eeeeeeeeeeeeeeeee. Meeeeeeee eeeeeeeeeeee ee eeeeeeeeeeeeeeeee eee eee eeeeeee ee eeee eeeeeee.

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 8/8e, 888.