Ketones divinyl, rearrangements with

Symmetrical ketones can be prepared in good yields by the reaction of organo-mercuric halides with dicobalt octacarbonyl in THF, or with nickel carbonyl in DMF or certain other solvents. The R group may be aryl or alkyl. However, when R is alkyl, rearrangements may intervene in the C02(CO)g reaction, though the Ni(CO)4 reaction seems to be free from such rearrangements. Divinylic ketones... 

The rearrangement of divinyl ketones to cyclopentenones (the Nazarov rearrangement) can be promoted with BF3-Et20. This transformation has recently been applied to good effect in the construction of the hydroazulene core found in guanacastepene. Other variants of the Nazarov reaction have been developed and are usually coupled with a second event, such as the reductive... 

Denmark and co-workers have published extensively on the use of (3-silyl substituted divinyl ketones (see 82) in the Nazarov cyclization. Such silyl groups control the collapse of the intermediate cyclopentenylic cations 84, and thus aid the regioselectivity of elimination, as well as the minimization of side reactions (secondary cationic rearrangements). Such stabilization derives from the known P-cation stabilizing effect of silicon, which through stabilization of 84, ensures maximum efficiency of the cyclization, with controlled formation of the final double bond. An important consequence of the final elimination step is that the double bond is placed in the thermodynamically less stable position (see 85). The most common Lewis acid used in the silicon-directed Nazarov cyclization is anhydrous iron(III) chloride, at temperatures below ambient. Alternatively, in cases where the... 

The mechanism of chemoselective copper(II)-mediated NazarovAVagner-Meerwein rearrangement sequence of divinyl ketones has been reported to involve an initial 4 r electrocyclization and proceed via two different sequential [l,2]-shifts, with selectivity that depends on either migratory ability or the steric bulkiness of the substituents at C( 1) and C(5) (Scheme 168). ... 

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