[431-03-8] · C4H6O2 · 2,3-Butanedione · (MW 86.09)
(cyclocondensations; reacts with Wittig reagents; condensations)
Alternate Name: biacetyl.
Physical Data: mp 2.4 °C; bp 88 °C/760 mmHg; d 0.981 g cm-3; fp <21 °C.
Solubility: sol water (25 g/100 mL); miscible with alcohol and ether.
Form Supplied in: yellowish green liquid; quinone odor.
Purification: dried over anhydrous CaSO4, CaCl2, or MgSO4, then vacuum distilled under nitrogen. The middle fraction is taken and stored at dry ice temperature in the dark (to prevent polymerization).
Handling, Storage, and Precautions: highly flammable, moderately toxic.
2,3-Butanedione (1) reacts with 1,3-dimethylurea in refluxing benzene containing 10% Trifluoroacetic Acid to form a bis adduct, 4,4´-methylenebis(1,3,5-trimethyl-4-imidazolin-2-one), whose structure has been confirmed by X-ray analysis (eq 1).1
Reaction of (1) with malononitrile catalyzed by Sodium Ethoxide furnishes the 1,5-dimethyl-3,7-dioxo-2,8-diaza-cis-bicyclo[3.3.0]octane-4,6-dicarbonitrile (eq 2).2 On the other hand, Piperidine-catalyzed condensation of (1) with 2-cyanacetamide forms 4,5-dimethyl-5-hydroxy-2-oxo-3-pyrrolinecarbonitrile (eq 3).3
Condensation of (1) with 4,5-diamino-2-thioxo-6-oxotetrahydropyrimidine,4 3,4-diamino-2-(methylthio)-5-cyanothiophene,5 and amidrazone,6 individually, affords 6,7-dimethyl-4-oxo-2-thioxotetrahydropteridine, 2-(methylthio)thieno[3,4-b]pyrazine, and triazine derivatives, respectively (eqs 4-6).
Condensation of (1) with an aldehyde (RCHO) in liquid Ammonia at 50-60 °C/20-25 atm furnishes the 4,5-dimethylimidazole (eq 7),7 whereas condensation with Hydroxylamine or its HCl salt in EtOH forms the corresponding 4,5-dimethyl-1-hydroxyimidazole oxide (eq 8).8
Biacetyl (1) with dihydrazino thiophosphites in a 1:1 ratio forms thiophosphatetraazacycloheptadienes (eq 9),9 whereas stirring with tris(trimethylsilyl) phosphite in benzene at rt furnishes the 3-trimethylsiloxy-2-butene-2-[bis(trimethylsilyl)] phosphate (eq 10).10
2,3-Butanedione (1) undergoes the Wittig reaction with propylenetriphenylphosphorane to furnish a mixture of cis- and trans-3-methyl-3-hexen-2-ones in a 45:55 ratio (eq 11),11 whereas stirring (1) with excess Cyanomethylenetriphenylphosphorane provides the bis Wittig adduct (E,E)-3,4-dimethylmucononitrile (eq 12).12
Reaction of (1) with Diazomethane in ether containing excess methanol or 1 mol of Boron Trifluoride provides 2-methyl-1-epoxybutan-3-one (eq 13),13 and with Diphenyldiazomethane furnishes 2-methyl-1,1-diphenyl-1,2-epoxybutan-3-one (eq 14).14
Reaction of (1) with p-cresol furnishes the benzofuro[3,2-b]benzofuran (eq 15).15
The dione (1) undergoes the Weiss-Cook process with Dimethyl 1,3-Acetonedicarboxylate to form tetramethyl 1,5-dimethyl-cis-bicyclo[3.3.0]octane-3,7-dione-2,4,6,8-tetracarboxylate (eq 16) in excellent yield.16
Acid-catalyzed reaction of (1) with cis-1,2-cyclohexanediol forms normal mono- and diacetals, whereas stirring with trans-cyclohexanediol provides a different bisacetal, represented in eq 17.17
Reaction of (1) with 2 equiv of allylzinc, prepared from Allyl Bromide, followed by acidic hydrolysis gives the g-ethylenic a-hydroxy ketone (eq 18).18
Thermal-mediated reaction of (1) with 1,1-diethoxyethene gives 2,2-diethoxy-4-acetyl-4-methyloxetane (eq 19);19 furthermore, (1) reacts with acetoxyphenylketene (generated in situ by reacting 2-acetoxyphenacyl chloride with Triethylamine in the cold) to give the b-lactone, which rearranges to a tricyclic orthoester lactone at temperatures above 130 °C (eq 20).20
Biacetyl (1) condenses with malonic acid in the presence of Titanium(IV) Chloride in pyridine-THF to furnish the a-carboxy-b,g-dimethyl-g-hydroxy-Da,b-butenolide (eq 21),21 a very useful precursor for the synthesis of eudesmane and certain elemane sesquiterpenes.
M. Sreenivasa Reddy & James M. Cook
University of Wisconsin-Milwaukee, WI, USA