3- cycloheptenone cyclopentanone

The oxyallyl zwitterion is involved in a mechanistic scheme to explain the production of cycloheptenones, cyclopentanones, and cyclopentenones by the reaction of aa -dibromo-ketones with iron carbonyl (Scheme 90). The intermediacy of organoiron halide complexes is proposed to account for... 

Cycloadditions. The reaction of-1 in CHjCl, with 1,3-dienes with zinc chloride as catalyst results in [3 + 4]cycloaddition to give cycloheptenones as major products. In some cases [3 + 2]cycloadducts are formed as minor products. Styrene derivatives react with 1 to form mainly cyclopentanones by [3 + 2]cycloaddition. 

Reaction with aja -dibromo ketones. Mechanistic aspects of this reaction have been discussed in detail. Use of this reaction to form 4-cycloheptenones and troponoids (5, 222-223 6, 195-196), tropane alkaloids (6, 223-224), 3-aryl-cyclopentanones, and cyclopentenones (4, 158) has been described in detail. 

Subsequent treatment of the resulting tetrahydrofuran derivative with Pd in the presence of dppe or PhjP led to isomerization (16 17) the final cyclopentanone product was contaminated by a minor amount of the isomeric cycloheptenone derivative. " Note that the thermal rearrangement of 16 proceeds as a [3,3] shift, affording the cycloheptenone isomer. 

Allyl vinyl ethers (66) undergo [l,3]rearrangements to give cyclopentanones (67) when heated with Pd° catalysts,in vivid contrast to the uncatalysed thermal rearrangement of compounds such as (66), which results in the formation of cycloheptenones. The recently developed oxyanionic Cope rearrangement of cyclononatrienols has been used by Paquette and Crouse as the key step in a brief synthesis of ( )-multifidene (68)/ Highly substituted alkylcyclopentenes may be prepared by [3 + 2]cycloadditions between allyl cations and olefins/ ... 

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