2,4-Pentanedione, 3-alkyl

Pentamethylenediazirine, 46, 83 2,4-Pentanedione, alkylation and cleavage with methallyl chlonde and potassium carbonate, 47, 87... 

Alkylation of the cyclization product 115 and the following hydrolysis gave 9-alkyl substituted 6-oxo-6,9-dihydroimidazo[4,5-/i]quinoline-7-carboxylic acid derivatives 119, compounds useful as antibacterials (no data) [80JAP(K)1], 4(7)-Aminobenzimidazole can react with 1,3-diketones as a bidentate nucleophile, but with 2,4-pentanedione in glacial acetic acid it gives a Combes product, l//-6,8-dimethylimidazo[4,5-/i]quinoline 120, accompanied by 4(7)-acetamido-benzimidazole (91T7459). 

MalONIC ACID, ETHYLHYDROXY, DIETHYL ESTER, BENZOATE, 45, 37 Mfsitaidehydf, 47, 1 Mesitylcne, condensation with dichloro methyl methyl ether, 47, 1 Methalljl chloride in alkylation of 2,4-pentanedione with potassium carbonate, 47, 87... 

Silver fluoborate, reaction with ethyl bromide in ether, 46, 114 Silver nitrate, complexing with phenyl-acetylene, 46, 40 Silver oxide, 46, 83 Silver thiocyanate, 45, 71 Sodium amide, in alkylation of ethyl phenylacetate w ith (2-bromo-ethyl)benzene, 47, 72 in condensation of 2,4-pentanedione and 1 bromobutane to give 2,4-nonanedione, 47, 92 Sodium 2 ammobenzenesulfinate, from reduction of 2 mtrobenzenesul-finic acid, 47, 5... 

The straightforward construction of substituted pyrone 4 proceeded as follows (see Scheme 6c). Alkylation of the monoanion of 2,4-pentanedione (8) with methyl iodide furnishes 3-methyl-2,4-pentanedione. Conversion of this substance into the corresponding dianion with sodium amide followed by selective carboxylation of the more basic site provides intermediate 7. Pyrone 4 is obtained after cyclization with l,l -carbonyldiimidazole and methylation of the resulting enol with dimethyl sulfate. 

Diazo-1,3-dicarbonyl compounds such as alkyl 2-diazo-3-oxobutyrates 57a, b and 3-diazo-2,4-pentanedione 57 c behave like the diazopyruvate 56, as far as their carbenoid cycloaddition behavior is concerned 114,130). 

Diiron enneacarbonyl, 50, 2J Diketones, from diazoketones and organoboranes, 53/ 82 3-DIKETONES FROM METHYL ALKYL KETONES 3-n-BUTYL-2,4-PENTANEDIONE, 51, 90 2,6-Dimethoxybenzaldehyde, by reduction of 2,6-dime thoxy-benzonitrile with Raney nickel alloy in formic acid,... 

Sodium amide, in alkylation, of di-phenylmethane, 48, 80 of ethyl phenylacetate with (2-bromoethyl)benzene, 47, 72 in condensation of 2,4-pentanedione and 1-bromobutane to give 2,4-nonanedione, 47, 92... 

Bi(OTf)3-Catalyzed Alkylation of 2,4-Pentanediones with Activated Alkenes 135... 

This first example of a Bi(OTf)3-catalyzed Friedel-Crafts alkylation originated in the following procedures, including benzylations of 2,4-pentanediones or hydroarylation and hydroalkylation reactions. A related procedure was simultaneously developed by Bonrath et al. [39]. The authors utilized Bi(OTf)3 in the synthesis of (all-rac)-a-tocopherol (Vitamin E) [39], Besides rare earth metal triflates, such as Ga(OTf)3, Hf(OTf)3, Sc(OTf)3 and Gd(OTf)3, Bi(OTf)3 was shown to be the most efficient catalyst for the Friedel-Crafts-type reaction between trimethylhydroquinone acetate 10b and isophytols 11a, b. With only 0.02 mol% Bi(OTf)3 (substrate to catalyst ratio 5,000 1) the desired a-tocopherols 12a and 12b were isolated in excellent yields (Scheme 10). 

Beside the Friedel-Crafts-type alkylation of arenes, the direct functionalization of 2,4-pentanediones is of great interest in Lewis acid catalysis. Although Pd-catalyzed Tsuji-Trost type allylations of 1,3-diketones are known, direct benzylation procedures catalyzed by Lewis acids are less explored [40-43]. Based on the previously described Friedel-Crafts alkylation of arenes and heteroarenes, the Rueping group developed a Bi(OTf)3-catalyzed benzylation of 2,4-pentanediones. Alcohols such as benzyl, allyl or cinnamyl alcohols were used as the electrophilic component to yield important 2-alkylated 1,3-dicarbonyl compounds. Initially, different Bi(III) salts were screened. In contrast... 

From a mechanistic point of view, it can be envisaged that this reaction proceeds via the desired benzylated pentanedione intermediate 14f. The subsequent intramolecular Friedel-Crafts alkylation of the electron-rich arene results in the quaternary benzyl alcohol II, which readily eliminates water to give the highly substituted indene 16 (Scheme 14). 

In addition to 1-phenylethanol and benzyl alcohol, cinnamyl alcohol has also been utilized as alkylating reagent. In contrast to the Bi(OTf)3-catalyzed Friedel-Crafts alkylation of benzyl alcohols, in which the corresponding acetate was shown to be more reactive than the free benzyl alcohol (Scheme 8), in this case the alkylation with cinnamyl alcohol or the corresponding acetate provided almost similar results. With 5 mol% BifOTfh. the desired allylated 2,4-pentanediones were isolated in good yields (Scheme 15). 

The concept of a diastereoselective Friedel-Crafts alkylation of a-chiral benzyl alcohols was first examined by Bach and coworkers [62, 63]. The initial protocol required stoichiometric amounts of strong Brpnsted acids like HBF4 and was followed by a more valuable methodology in which catalytic amounts of AuC L were employed for the diastereoselective functionalization of chiral benzyl alcohols [64], Beside arenes, allyl silanes, 2,4-pentanediones and silyl enol ethers have been used as nucleophiles. Depending on the diastereodiscriminating group and on the catalyst (Brpnsted or Lewis acid), the authors observed either the syn or the anti diastereoisomer as the major product. 

P-DIKETONES FROM METHYL ALKYL KETONES 3-w-BUTYL-2,4-PENTANEDIONE... 

This procedure for the acetylation of methyl alkyl ketones to form /3-diketones is a modification5 of an earlier procedure, which used boron trifluoride gas as the catalyst.6 3-n-Butyl-2,4-pentanedione has also been prepared by the acetylation of 2-heptanone catalyzed with boron trifluoride gas,7 by the thermal rearrangement of the enol acetate of 2-heptanone,7 and by the alkylation of the potassium enolate of 2,4-pentanedione with n-butyl bromide.8... 

DIKETONES from methyl alkyl KETONES 3-n-BUTYL-2,4-PENTANEDIONE, 51, 90... 

Methyl-2,4-pentanedione, a2-alkylated 1,3-diketone, behaves like simple unsubstituted analogues (Scheme 59). This asymmetric hy-... 

---