Acid chlorides divinyl ketones from

The acid-catalysed ring-closure of divinyl ketones to cyclopentenones (equation 6), the Nazarov reaction6-8, represents a conrotatory electrocyclization of 4jr-cyclopentadienyl cations. The conrotatory course of the reaction was confirmed for the case of the dicyclo-hexenyl ketone 7, which yielded solely the tricyclic ketone 8 on treatment with phosphoric acid (equation 7)3b. Cycloalkanocyclopentenones 10 with c/s-fused rings are obtained from the trimethylsilyl-substituted ketones 9 (n = 1, 2 or 3) and iron(III) chloride and... 

Disilylalkenes provide an access to acylated ( )-vinylsilanes. 1,3-Disilylpropenes tend to behave as 3-silylpropenes towards acylation, because of the lability of the a-silyl ketone formed initially.72 Divinyl ketones are isolated from reactions with unsaturated acid chlorides.73 Since these are cyclized under the reaction conditions, they are presumably formed during work up, possibly from silyl dienolate intermediates (Scheme 12). 

The same approach was also used to prepare the truncated YCK analogues, 116-119 (69,70). Cheng also prepared inverto-YCK (124) from the add chloride 120 (Scheme 9). The key steps involved the coupling of 3-indolezinc reagent with the acid chloride 120, followed by Nazarov cyclization of the divinyl ketone 121, to the tetracyclic ketone intermediate, 122. The indolyl moiety was introduced by Pd(0)-mediated cross coupling between the indolezinc reagent and the acetate derivative, 123 (71). 

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... 

High yields of symmetrical divinyl ketones are obtained stereospecifically from the reaction of vinylmercurials, lithium chloride, and 0.5 mol% of [Rh(CO)2Cl]2 in THF under carbon monoxide at atmospheric pressure and at room temperature (e.g. Scheme 94). The products, sensitive to both acid and base, are easily isolated from the neutral reaction medium. 

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