Classical Nazarov reaction

Subsequent investigations by Denmark have shown that vinylsilanes can direct the course of Nazarov-type cyclization reactions. Once again the regiochemical outcome is controlled by the -effect as substitution takes place at the carbon bearing the silyl group (Scheme 7). This clever modification provided a solution to the serious problem of double bond isomerization that is frequently observed in the classical Nazarov reaction. Treatment of the enone (11) with commercially available anhydrous iron(III) chloride (FeCb) promoted cyclization to give one double bond isomer of the m-hydrindinone (12) in excellent yield. Table 2 summarizes a representative collection of cyclization reactions catalyzed by FeCb. 

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