Acetoacetylation with diketen

Hydroxyalkyl acrylates and polyols are acetoacetylated with diketene to give comonomers used in adhesives, polymers, and coatings, especially the new low solvent coatings, and for emulsion polymeri2ation. The most widely used compound is 2-acetoacetoxyethyl methacrylate (A ARM A) (152). 

In the first step, Rink amide AM PS Resin was acetoacetylated with diketene. Treatment with primary amines resulted in polymer-bound enaminones which then underwent a Hantzsch reaction [30] with l,4-dibromo-2,3-butanedione under formation of 5-(2-bro-moacetyl)pyrroles which could be cleaved from the resin with 20 % TFA/CH2C12. 

Mercuric acetate Mercuric salts as catalysts N-Acetoacetylation with diketene... 

Acetoacetic ester s. y -Keto-carboxylic acid esters C-Acetoacetylation with diketene 24,708 N-Acetoacetylation with diketene 24, 334, 708 Acetone as reagent (s. a. under Sensitizers) 22, 324 Acetonitrile... 

Mono condensation products such as 14 have also been used as a diazo compo-nent , or as a coupling component after acetoacetylation with diketene, to prepare a variety of monoazo and disazo pigments. 

N-Acetoacetylation with diketene of N-silylcarboxylic acid amides... 

Ketcha and Wilson reported the solid-phase version of the classic Nenitzescu indole synthesis in a process involving initial acetoacetylation of ArgoPore-NH2 resin with diketene to afford a polymer bound acetoacetamide <00TL6253>. Formation of the corresponding enaminone 102 via condensation with primary amines in the presence of trimethylorthoformate followed by addition of 1,4-benzoquinones 103 leads to formation of polymer bound 5-hydroxyindole-3-carboxamides 104 which could be cleaved from the resin using TFA yielding the indoles 105. 

Aliquat is an efficient catalyst for the acetoacetylation of amines by diketene. The initially formed amides react with an excess of the diketene to form, after cyclization of the secondary product, 1-substituted 3-acetyl-4-hydroxy-6-methylpyrid-2-ones [39]. Amides react under similar conditions with diketene to form A-acyl aceto-acetamides, which react further with a second molecule of diketene to yield, after cleavage of the A-acyl group, 3-acetyl-4-hydroxy-6-methylpyrid-2-one [39]. 

Figure 4.4 Acetylation of wood with ketene gas (a) and acetoacetylation of wood with diketene (b).

N-Acetoacety lotion. The N-acetoacetylation of amides with diketene is markedly improved if it is carried out in the presence of iodotrimcthylsilanc (generated in situ). The reactive reagent is probably a. 

Acetoacetylation with DMAP.1 Alcohols (even lerf-ones) undergo acetoacety-lation when treated with diketene in the presence of DMAP (55-100% yield). The reaction generally occurs at room temperature. 

Other interesting reactions with diketene include its use in a Friedel-Crafts-type acetoacetylation of ferrocene (Scheme 14) and a l,l -diphosphaferrocene <20010M4448>. When boron trifluoride was used as the Lewis acid, BF2 chelates of the acetoacetylated metallocenes were formed. 

When diethyl malonate is the diketone component, the ester (135) is first formed, which then cyclizes to the expected (136). Reaction of (131) with diketene gives a mixture of (137) and (138), the latter on acid cyclization also yields (134). This rearrangement is by a 1,3-shift of the acetoacetyl group to give the transient imine followed by cyclization. Similar rearrangements are known. Compound (139), the 7-one isomer of (134), is obtained from the reaction of (131) with a-bromocrotonic acid (76JHC291). 

Acetoacetylation. Mercuric salts, particularly mercuric acetate, are effective catalysts for the acetoacetylation of weakly nucleophilic compounds (e.g., urea, diphenylamine,p-nitroaniline, phenol) with diketene at room temperature.45... 

Reaction of 1 with diketene 404 in the presence of sodium hydroxide in tetrahydrofuran gave 2-acetoacetyl dimedone 405. Cyclization of which to the benzopyran-4,5-dione 406 was performed with acid (73CPB1840). 

Xylidine is used in the preparation of N-acetoacetyl-2,4-xylidide (AAX), an intermediate in pigment manufacture it is accessible by the reaction of 2,4-xyli-dine with diketene. 

The acetoacetyl derivatives are obtained by the reaction of the amine with diketene . In the case of amino acid ester hydrochlorides the presence of one equivalent of sodium methoxide or of a tertiary base is necessary. The group is removed by applying the conditions of the Knorr synthesis of pyrazol derivatives from various /3-keto esters and their derivatives . The protecting group is removed in acetic acid by using an equimolar amount of phenylhydrazine (reaction 3). 

The N-benzyloxycarbonyl derivatives of serine and threonine can be converted into their t-butyl esters, using isobutene and an acid catalyst, only after protection of the alcohol group by reaction with diketen to give the o-acetoacetyl derivatives. The alcohol group can then be unmasked by treatment with hydrazine. 

Pyrrole itself undergoes a,a -disubstitution. Diazo-acetoacetic ester can be used in this reaction. The mechanism of this reaction, which may be a radical substitution or involve the intermediate formation of a ketene, is uncertain, but it is interesting to note that a number of pyrroles react readily with diketene, giving G-acetoacetyl derivatives, and that ketene converts 2,4-dimethylpyrrole into 2-acetyl-3,5-dimethylpyrrole . In view of these results, the earlier report that diphenylketene converted pyrrole into 1-diphenylacetylpyrrole must be questioned. 

Recently, 1-ethoxyvinyl acetate has been proposed as a novel and reliable acyl donor for the enzymatic resolution of alcohols (Scheme 24) in a lipase-catalyzed irreversible transesterification procedure [135]. A similar protocol has been utilized for the irreversible acetoacetylation of alcohols with diketene in the presence of lipases in organic solvents [136,137] and the reaction has been reported to proceed with high enantioselectivity [136], as shown in Scheme 25. 

Acetoiicetyliition Reactions. The best known and commercially most important reaction of diketene is the aceto acetylation of nucleophiles to give derivatives of acetoacetic acid (Fig. 2) (1,5,6). A wide variety of substances with acidic hydrogens can be acetoacetylated. This includes alcohols, amines, phenols, thiols, carboxyHc acids, amides, ureas, thioureas, urethanes, and sulfonamides. Where more than one functional group is present, ring closure often follows aceto acetylation, giving access to a variety of heterocycHc compounds. These reactions often require catalysts in the form of tertiary amines, acids, and mercury salts. Acetoacetate esters and acetoacetamides are the most important industrial intermediates prepared from diketene. 

The amine or amide (50 mmol) and Aliquat (0.81 g, 2 mmol) in PhMe (20 ml) are stirred at 70-90 °C and diketene (6.73 g, 80 mmol) is added dropwise. The mixture is stirred for 8-10 h and then cooled, filtered, and evaporated. The residue is extracted with Et20 (3 x 25 ml) and the extracts are evaporated to yield the acetoacetylated product... 

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