1.3- dicarbonyl compounds reaction with phenyl

The O-phenylation reaction with tetraphenylbismuthonium trifluoroacetate (6) was also extended to enols. A series of enolised dicarbonyl compounds were 0-phenylated in modest to moderate yields with this reagent under neutral or acidic conditions, the best yields being again obtained under acidic conditions. ... 

Ketones such as methyl cyclohexyl ketone 1284 react with DMSO/TCS 14, via their enol form, to give 21% of the chloroketone 1285 a and 63% of the a-methyl mercaptoketone 1286 [70]. Reaction of 1284 with DMSO/MesSiBr (TBS) 16 affords 85% of the bromo compound 1285 b and 12% hexahydrophenacyl bromide 1287 but no 1286 [71]. Whereas reaction of tra s-4-phenyl-3-buten-2-one (benzalacetone) 1288 with DMSO/TCS 14 gives 81% of the sulfonium salt 1289 [70], the y9-dicar-bonyl compound ethyl acetoacetate furnishes 69% of 1290 [70]. In contrast with DMSO/TCS 14, the combination DMSO/TBS 16 effects selective monobromina-tion of y9-dicarbonyl compounds [71] (Scheme 8.28). 

Cyclopentene annelation.1 The reaction of the anion of a 1,3-dicarbonyl compound with l-decynyl(phenyl)iodonium tetrafluoroborate results in an annelated 3-pentylcyclopentene in reasonable yield. The product is considered to result from... 

General methods for preparation of imidazolidin-4-one-2-thiones include the reaction of thioureas with a-dicarbonyl compounds,37,38 with ethyl phenylpropiolate,39 and with phenyl chlorothiolacetate,40 and cyclization in acid of l-(carbethoxymethyl)-2-thioureas.41 The analogous reaction of a-diearbonyl compounds with selenoureas produce imidazolidin-4-one-2-selones.42 Berlin and Levi43 utilized the acid-catalyzed cyclization of l-aryl-3-carbalkoxymethyl-2-thioureas to produce 3-arylimidazolidin-4-one-2-thiones (23). 

It has been shown that selective a-vinylation of enolate anions derived from 1,3-dicarbonyl compounds can be achieved by reaction with 4-/-butyl-1 -cyclohexenyl-(aryl)iodonium and 1-cyclopentenyl(aryl)iodonium tehafluoroborates without competing a-arylation, provided that the alkenyliodonium salt used bears a / -mcthoxyphcnyl, rather than phenyl, group.24... 

Enolate anions derived from various 1,3-dicarbonyl compounds can be viny-lated with cyclohexenyl- and cyclopentenyl- iodonium salts (Scheme 27) [50]. The vinylation of enolate anions 58 in these reactions is frequently accompanied by the formation of the phenylated dicarbonyl compounds however, the selectivity of these vinylations can be improved by using alkenyl(p-methoxyphenyl)-iodonium salts instead of 57. 

Alkynyl(phenyl)iodonium salts can be used for the preparation of substituted alkynes by the reaction with carbon nucleophiles. The parent ethynyliodonium tetrafluoroborate 124 reacts with various enolates of /J-dicarbonyl compounds 123 to give the respective alkynylated products 125 in a high yield (Scheme 51) [109]. The anion of nitrocyclohexane can also be ethynylated under these conditions. A similar alkynylation of 2-methyl-1,3-cyclopentanedione by ethynyliodonium salt 124 was applied in the key step of the synthesis of chiral methylene lactones [110]. 

When / -dicarbonyl enolates are allowed to react with alkynyliodonium salts, typically in ter/-butyl alcohol or THF, alkynyl- and/or cyclopentenyl- -dicarbonyl compounds are obtained. The product compositions are largely regulated by the migratory aptitude of R in the alkynyl moiety and the availability of alkyl side chains for the MC-insertion (MCI) pathway (equation 45). These divergent modes of reactivity are nicely illustrated by the reactions of the 2-phenyl-1,3-indandionate ion with ethynylfphenyl)- and 4-methyl-1-hexynyl(phenyl)iodonium tetrafluoroborates (equation 1 15)27 2. 

Reactions of unsymmetrical methylene 1,3-dicarbonyl compounds with enol ethers have been investigated by Yamauchi et al. [137]. As we have mentioned earlier, the a,/ -unsaturated ketone moiety in alkylidene-/ -ketoesters reacts exclusively as the oxabutadiene. However, high regioselectivity is also observed with mixed alkyl-phenyl-1,3-diketones with exclusive reaction of the aliphatic carbonyl group, whereas in alkylidene-1,3-dicarbonyl compounds bearing an aldehyde and a keto-moiety, the a,/J-unsaturated aldehyde reacts preferentially as oxabutadiene, but not exclusively [130a]. 

Treatment of enolate anions derived from 3-dicarbonyl compounds with either ethynyl(phenyl)iodo-nium tetrafluoroborate (16) or with ethynyl-lead tetraacetate provides a neat and direct synthesis of a-ethynyl-l,3-dicaibonyl compounds. The former reaction probably proceeds via 1,2-hydrogen migration of an alkylidenecarbene intermediate (see Scheme 34). 

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