Diketene, reaction with

Diketene, reaction with tert-butyl alcohol to give tert-butyl acetoace-tate, 42, 28... 

Chemical Properties. Diketene is a reactive and versatile compound which can undergo reaction with a large variety of compounds. These reactions have been reviewed comprehensively (1,5,6,96). 

Diketene reacts with imines to give l,3-oxa2inones (16) (105). This reaction has been used in the synthesis of the tranquili2er Keta2olam... 

Other Reactions of Diketene. Diketene reacts with elemental chlorine to give 4-chloroacetoacetyl chloride [41295-64-17, which can further react to the corresponding esters (111). 

BenZimidaZolones. This class of pigments derives its name from 5-aminobenzimidazolone/Pj5 -2J-< 7 which upon reaction with diketene or 2-hydtoxy-3-naphthoyl chloride leads to compounds which can be coupled with a variety of diazotized amines. 

Coumarin can also be formed by the reaction of phenol with diketene (40). Similarly, diphenols can react with hydroxycarboxyUc acids or beta-ketoesters to give hydroxycoumaria derivatives. The reaction of resorciaol with malic acid produces umbeUiferone (7-hydroxycoumaria) and its reaction with ethyl acetoacetate gives beta-methylumbeUiferone (7-hydroxy-4-methylcoumaria). 

Reaction with diketene affords the corresponding /3-diketo compound 124. 

Initial polymer hydrolysis products are the diol or mixture of diols used in the reaction with the diketene acetal, and pentaerythritol dipropionate, or diacetate if 3,9-bis(methylene-2,4,8,10-tetraoxaspiro-[5,5Jundecane) was used. These pentaerythritol esters hydrolyze at a slower rate to pentaerythritol and the corresponding aliphatic acid (13). 

Hayashi et al. have reported a novel Knoevenagel-type reaction with titanium enolate 70 derived from diketene 69 as the C4 unit source (Scheme 26).76 In contrast to the conventional Knoevenagel reaction (basic conditions), this transformation proceeds under mildly acidic conditions and provides higher yields and better E Z ratios. 

The synthesis of the coupling component 5-acetoacetylaminobenzimidazolone (25) corresponds to the preparation of acetoacetarylides (Sec. 2.1.2) from 5-aminobenz-imidazolone by reaction with diketene or acetoacetic ester ... 

Since reaction of wood with acetic anhydride leads to the formation of acetic acid by-product, which must be removed from the wood, there has been some interest in the use of ketene gas for acetylation (Figure 4.4a). Ketene, for reaction with wood, is produced by pyrolysis of diketene. Provided that the wood contains no moisture, no acetic acid by-product is produced. However, ketene presents handling problems it is very toxic and explosive, and it also has a tendency to dimerize. A comprehensive series of studies of ketene-based acetylation has been performed in Latvia and this work has been reviewed by Morozovs etal. (2003). Hardwoods have been found to be more reactive to ketene than softwoods and the optimal temperature for reaction has been determined as 47 °C. Application of vacuum and treatment of wood with ammonia solution has been used to remove the excess ketene. The reaction of wood with liquid diketene was also studied, with a WPG of 35 % being obtained after reaction for 3 hours at 52 °C. 

With diketene, intermediates of type (III) were isolated and subsequently cyclized under basic conditions following step (b). In the case of 3-oxo-carboxylic acid esters or 3-acyl Meldrum s acids, cyclization step (b) immediately follows reaction step (a), if a slight excess of amine is employed (85TH1 87TH1). Note that conversion of (III) to (V) involves the (IH)-enol (Table I cf. 75BSF2731). The relatively low yield in the case of malonic acid ester, as well as the failure of the reaction with the non-enolizable diphenyl phosphinylacetic ester and cyanoacetate, points to the participation of an enol structure of (III). 

With formaldehyde, diketene reacts quite vigorously in water solution without acid catalysis, to give carbon dioxide and 2,6-heptanedione, isolated in 40% yield (75JOC675). This reaction can be explained analogously, with an initial electrophilic attack of the formaldehyde carbon atom on the exocyclic methylene carbon atom of the diketene, followed by ring opening and then reaction with a second molecule of diketene (equation 25). 

In a similar fashion 2-aminothiophenol can be reacted with 1,3-bis carbon electrophiles to give various types of 1,5-benzothiazepine. Thus the benzo analogues of (408) and (409), e.g. (410), are prepared by parallel routes, reaction with 1,3-diphenylpropynone gives (411), reaction with /3-ketoesters gives products of type (412), reaction with diketene gives (413), and the reaction with methyl 3-arylglycidates gave (414) which could not be dehydrated. 

In another cyclization procedure for the 1,5-benzodiazodne system, the nitriles (296) are converted to the aminodihydrodiazocines (297) (79CPB2589). Attack of nucleophiles on (297) occurs at the N-5—C-6 bond to give the 3,4,5,6-tetrahydrodiazodnes (298) with NaBH4 and the jS-aminoethylquinazolines (301) on hydrolysis. The diazocines (297) behave as typical amidines. Oxidation leads to the amidoximes (300) which on hydrolysis are converted to 2,1-benzisoxazoles (302), and reaction with diketene leads to the fused pyrimidinones (299 and l-methyl-3-one isomer) (79CPB2927). 

The preparation of dihydro-4//-l,3-oxazinones (166) from mono-239,240 or disubstituted307 thiopseudoureas has been accomplished by their reaction with diketene. In one case,239 a 2-alkylthio intermediate in the... 

Oxazin-4-ones and -thiazin-4-ones are well represented in the chemical literature. Thiazin-4-ones can be synthesized from 1,3-oxazinium salts by the action of hydrogen sulfide and potassium carbonate (81H(15)85l) and oxazin-4-ones are obtained by cycloadditions between isocyanates and ketenes (Scheme 73), or alkynes (Scheme 74), or between nitriles and acylketenes (Scheme 75). Similarly diketene is often used and affords oxazin-4-ones by its reactions with imidates and cyanamides (Scheme 76) (80H(14)1333>. 

Diketene is very useful in synthesis, particularly through its reactions with alcohols and amines to give derivatives of 3-oxobutanoic acid ... 

They also described the reaction of diketene with N,N-dimethylurea in acetic acid, yielding 50 (see also Ahmed et a/.177). Gunar et a/.178 used diketene in the reaction with cyanic acid (see also Ozaki179), thiocyanic acid, ethyl urethane, and N,N -disubstituted ureas in acetic acid medium to obtain 50. When a 2-thiono derivative was obtained from thiocyanic acid, as in Eq. (37), they desulfurized it with mercuric acetate. 

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