Cyclopentenones annulation

McKervey and coworkers have developed an elegantly simple pathway for the conversion of m-bicyclo[3.3.0]octane-2,6-dione to (C2)-C2o-hexaquinane diketone 858 (Scheme CII) Twofold cyclopentenone annulation and hydrogenation rapidly led to the tetraquinane 857. Repetition of the same steps then afforded 858, the x-ray analysis of which showed the molecule to have an opened out conformation as the direct result of severe intramolecular overcrowding. 

A new synthesis of ( )-actinidine has been reported it is interesting in that it has, as its key step, the thermal intramolecular cycloaddition of an acetylenic pyrimidine.34 A further synthesis of ( )-muscopyridine, based on a regioselective cyclopentenone annulation, has been described.35... 

Likewise, 1,1-dichloroallyllithium preferably reacts C-l with electrophiles63) as is seen from the results of Hiyama et al, who used this reagent for cyclopentenone annulation 64) (Eq. (59)). 

Both (+)-nootkatone (566) and its (+)-4-isomer (565) have been synthesized from (+)-nopinone (564) (Scheme 69). ° On the other hand, Hiyama et have used a completely different approach for the synthesis of nootkatone (566) (Scheme 70) which involves as a key step the acid-induced cyclopentenone annulation. In an alternative route to eremophilane and valencane sesquiterpenes, NM et have used a stereoselective intramolecular Diels-Alder... 

A significant advance in the use of Friedel-Crafts acylation of alkenes to prepare divinyl ketones was the employment of vinylsilanes to control the site of electrophilic substitution. Two groups have developed this approach to cyclopentenone annulation using slightly different strategies. In the method described by Magnus the reagent vinyltrimethylsilane (80) is used primarily as an ethylene equivalent (equation 44). The construction of bicyclic systems followed readily as Nazarov cyclization proceeded under the reaction conditions. Tin(lV) chloride was found to be the most effective promoter of the overall transformation. As expected the position of the double bond is thermodynamically controlled. 

KHAND PAUSON Cyclopentenone Annulation Cyclopemenone synthesis from carbon monoxide acetylene and olefins, cobalt carbonyl catalyzed. 

Irie and co-workers have reported a synthesis of ( )-tecomanine (55) based on a cyclopentenone annulation of 1,4-diketones (Scheme 17) (205). Treatment of 1,3-dimethylpiperidone (246) with lithium diisopropylamide (LDA) and 2-nitro-2-butene, and reaction with 10% hydrochloric acid (Nef reaction) afforded the substituted piperidine 1,4-diketone 247 (a homolog of 230 in Scheme 14) in 87% yield. Reaction of the mixture of isomers with K3PO4 at 55°C for 55 h gave a single cyclized product 248, whose... 

In a similar way, cA-fused bicyclie systems are obtained via stereoselective nickel-mediated cyclopentenone annulation to cyclic 3-haloalkenes with alkynes and carbon monoxide57. 

Vinylsilanes also find use as intermediates for cyclopentenone annulation of a, (3-unsaturated acid chlorides under Lewis acid conditions.One such example is shown in Scheme A novel methylenecyclopentane synthesis depends on... 

Danishefsky et aC have presented in full their syntheses of ( )-coriolin (111) and ( )-coriolin-B, which feature the cyclopentenone-annulation procedure (112) - (113) at the outset. Japanese workers have also achieved total syntheses of ( )-coriolin in which one key step is the conversion of 1,3-cyclo-oc-... 

The promise suggested for the recently described (Vol. 4, p. 252) method of cyclopentenone annulation, based on vinyl silane directed Friedel-Crafts acylation followed by Nazarov cyclization (Scheme 7) has been fully vindicated with... 

One such example is shown in Scheme 9, where intermediate 20 was swiftiy taken to 37 in a one-pot deprotection-tosylation-intramolecular y-alkylation mechanism utilizing tosyl fluoride. The resulting terminal olefin, when subject to Tsuji-Wacker oxidation conditions, furnished methyl ketone 38, which when exposed to strongly basic conditions triggered the Robinson annulation sequence, providing us with a cyclopentenone annulated analog 39. 

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