2- cycloheptenone 2- cyclohexanone

Bromocyclohept-2-en-l-one (40) should be convertable to cycloheptenone (41) by hydrogenolysis of the bromine atom. Thus the process (34) - (41) provides a general method for conversion of symmetrical cyclohexanones to cycloheptenones. 

Ring expansion (7, 153-154). Details are available for expansion of cyclohexanone to 2-cycloheptenone via cyclopropanation of enol silyl ethers (equation 1). The report includes six other examples of this method yields range from 80 to 98%. In all cases the more highly substituted C C bond of the cyclopropane ring is cleaved by FeCI,.1... 

Organometallic methods, with the possible exception of those involving the stoichiometric generation of enolates and other stabilized carbanionic species 140], have seldom been used in carbohydrate chemistry for the synthesis of cyclohexane and cyclopentane derivatives. The present discussion will not cover these areas. The earliest of the examples using a catalytic transition metal appears in the work of Trost and Runge [41], who reported the Pd-catalyzed transformation of the mannose-derived intermediate 22 to the functionalized cyclopentane 23 in 98% yield (Scheme 10). Under a different set of conditions, the same substrate gives a cycloheptenone 24. Other related reactions are the catalytic versions of the Ferrier protocol for the conversion of methylene sugars to cyclohexanones (see Chap. 26) [40,42,43]. 

Different cyclohexanones 298 reacted with 297 to give adducts 299 and, after treatment with mercury(II) chloride, cycloheptenones 300, resulting from a ring enlargement reaction (Scheme 78)476,477. 

Yang, S., Hungerhoff, B., and Metz, P. 1998. A short conversion of cyclohexanones to cycloheptenones. Tetrahedron Lett 39, 2097-2098. 

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