Someone really should take a closer look at this reaction, which is the addition of benzylmagnesium chloride to acetylacetone. The authors seems to have a real tough problem on their hands - their desired addition product is violently unstable, and decomposes to phenylacetone upon the slightest treatment with acid. They aren't explicitly mentioning any yields, but 96 mL benzyl chloride, 19g Mg and 40 mL acetylacetone gives 140 mL of "mainly" IV, which upon heating decomposes to "mainly" phenylacetone (IX). Shouldn't be too bad, all in all - and why shouldn't the reaction be extendable to substituted P2P's?Mono- and bis-Addition Products of Benzylmagnesium Chloride to AcetylacetoneA. Barabás and A. T. BalabanTetrahedron 27, 5495-5503 (1971)
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/p2p.acac-grignard.pdf)
AbstractThe addition of excess benzylmagnesium chloride to acetylacetone affords a mixture of mono- and
bis-addition products, whose relative yields suggest that the mono-addition isa reaction of the enol tautomer and the
bis-addition a reaction of the diketo-tautomer. 4-Benzyl-4-hydroxypentan-2-one (
IV), the primary mono-addition product, is easily dehydrated to 5-phenyl-4-methyl-3-pentene-2-one (
XI), which was isolated and characterized. This dehydration is a delicate operation; in some runs, only the splitting product, phenylacetone (
IX) could be isolated.
Experimental Addition of acetylacetone to Benzylmagnesium chlorideBenzylmagnesium chloride was prepared as usual from 19.2 g Mg turnings and 96 ml (0.8 moles) PhCH
2Cl in ether. To this solution 40 ml 10.4 moles) of acetylacetone in 50 ml ether were introduced dropwise under vigorous stirring ata rate which allows the mixture to reflux gently. The stirring under reflux was maintained for an additional 6 hr period by heating. The mixture was then cooled by an ice-salt bath and 200 ml of ice-cold. sat. NH
4Cl(aq) added under vigorous stirring continued till nearly all solid material dissolved. The cold solution was filtered and the precipitate washed several times with fresh NH
4Cl(aq). The ethereal layer of the filtrate was separated and the aqueous phase extracted with ether. Combined organic layers were dried (Na
2SO
4) and the ether evaporated at room temperature. About 150 ml of yellowish oil was obtained. consisting mainly of 4-benzyl-4-hydroxypentan-2-one (
IV), which could not be purified because it underwent dehydration.
Splitting of benzyl-methyl-acetonyl carbinol (IV) to benzyl methyl ketone (phenylacetone, IX)By heating product
IV without I
2 (or in a few irreproducible runs even with I
2), 40 ml of a different distillate, b.p. 100-130°C/10mmHg was obtained. Its main component
IX could be obtained by refractionation at 80°C/6mmHg or 71°C/3mmHg and yielded on treating with DNPH only a yellow adduct, which after several recrystallizations from dioxane melted at 156°C. Literature mp for
X, 152-4°C.