Ketenes ketoester

Of course, the use of tris(trimethylsilyl) phosphite213 214 provides facile access to the free a-hydroxyphosphonic acids. These silyl reagents have been used for the preparation of a wide range of a-substituted phosphonates and -phosphonic acids, starting with ketene,215 a-ketophosphonates,216 ketoesters,217 218 and a,P-unsaturated carbonyl compounds,207/219-221 as well as simple aldehydes and ketones.205 210/219 224 Their use for the preparation of compounds of significant biological interest has been reviewed.125... 

Reaction of 4a with TiCl4 was carried out in the presence of siloxyalkene 3 as nucleophile and the results are summarized in Table III. In the reaction with ketene silyl acetals 3a and 3e at -78 °C, y-ketoesters 15a and 15e were obtained instead of chloride product 8 which is a major product in the absence of 3. Formation of product 15 is likely to result from trapping of alkylideneallyl cation 5 with 3 at the sp2 carbon. In contrast, the reactions with silyl enol ethers 3f and 3g gave no acyclic product 15, but gave cyclopentanone derivatives 16-18. The product distribution depends on the mode of addition of TiCl4 (entries 4-7). 

KETENE, feef-butylcyano-, 55, 32 37, 38 Ketene 1 1-dimethylpropylcyano-, 55, 38 7-KETOESTERS, 58, 79, 81, 82 7-KETOESTERS TO PREPARE CYCLIC DIKETONES, 58, 83 KETONE terf-butyl phenyl, 55, 122 Ketone, methyl ethyl- 55, 25 Ketone, methyl vinyl, 56, 36 KETONES, acetylenic, 55, 52 Ketones, alkylation of, 56, 52 KETONFS aromatic, aromatic hydrocarbons from 55, 7... 

Schlessinger has shown that the addition of ester enolates to sulfur stabilized acceptors, e.g. ketene di-thioacetal monoxide (151) and methyl a-(methylthio)acrylate (187), is highly efficient for the synthesis of Y-ketoesters.148 Similarly, Ahlbrecht and Seebach have reported that amide and ester enolate additions to nitrogen stabilized acceptors, e.g. nitroalkenes (40) and 2-(/V-methylanilino)acrylonitrile (59 Scheme 72), are highly efficient.149... 

Of course, one can also carry out Wolff rearrangements in the presence of nucleophiles other than H20. Ketenes are then produced in their presence, and the addition products of these nucleophiles are therefore isolated. Figure 14.28 shows how one can add an alcohol to a ketene in this way. An alcohol addition to a ketene is also involved in the /3-ketoester synthesis discussed in Side Note 6.2. 

Ketene acetal sulfoxide 30 has been used as a chiral ketoester ketene acetal equivalent, because it undergoes a ready enantiocontrolled reaction with cyclopentadiene at -78°C in the presence of BF3 yielding a 96 4 mixture of endo and exo adducts with complete n-facial selectivity (Scheme 15) [44]. The endo selectivity decreased with other catalysts, but the 7r-facial selectivity remained complete, whereas under thermal conditions (139 °C, 15 h) a mixture of the four possible adducts was obtained. The adduct 31 was transformed into (+)-(lRy4R)-norbornenone in a four-step sequence. 

A unique thermal cleavage of certain cyclopropyl ketoesters has been reported by Berkowitz ". The intermediacy of a ketene and its rearrangement together with carbon monoxide loss is postulated. This sequence has led on to the preparation of ds-jasmone (equation 58) ... 

Conjugated ketenes. a-Diazo-y.S-unsaturated P-ketoesters undergo rearrangement to ketenes which enter Diels-Alder reactions as dienes toward electron-rich alkenes. Substituted phenols are acquired. 3-Acyloxy-2-chloro-2-cyclohexenones are formed when 2-diazocyclohexane-l,3-diones are treated with acid chlorides in the presence of Rh COAc),. ... 

The ketene 0,0-acetals 83 were prepared from the corresponding bromo derivatives by reaction with strong base A diastereoselective synthesis of the trans- and cis 84 was carried out. Condensation of substituted aminothiophenols and 2-arylidene-l-tetralone afforded 1,4-thiazepines 85. Condensation of o-phenylenediamines with P-ketoesters or 1,1,1-trifluoromethyl-3-(isobutoxymethylene)-2-propanones gave 84. ... 

Several routes to this class of compounds have been reported, such as (a) crossed Claisen condensation reactions (50-53) (b) acylation of the anion derived from ethyl fluoroacetate (54) or self-condensation of the anion derived from ethyl bromofluoroacetate (55) (c) electrophilic fluorination of the anion of p-ketoesters (56,57) (d) acylation-hydrolysis of fluoroolefins (58) and (e) acylation of fluorine-containing ketene silyl acetals (Easdon, J.C., University of Iowa, unpublished data). The limitations associated with these methods and the success achieved in the alkylation-hydrolysis of a-fluoro phosphorus ylides prompted us to examine acylation-hydrolysis of these a-fluoro ylides as a general route to 2-fluoro-3-oxoesters. 

Modified Claisen condensation. Silyl ketene acetals and methyl esters (important ) react in the presence of Me3Al in toluene to afford mixed methyl/silyl acetals of (3-ketoesters. 

Rubottom oxidation reactions have been conducted on enolsilanes derived from a number of different carbonyl derivatives including carboxylic acids and esters.15 For example, the Rubottom oxidation of bis(trimethylsilyl)ketene acetal 30 provided a-hydroxy carboxylic acid 31 in 81% yield. Use of alkyl trimethylsilyl ketene acetal substrates generates a-hydroxy esters, as seen in the conversion of 32 to 33.16 The synthesis of 3-hydroxy-a-ketoesters (e.g., 36) has been accomplished via Rubottom oxidation of enolsilanes such as 35 that are prepared via Homer-Wadsworth-Emmons reactions of aldehydes and ketones with 2-silyloxy phosphonoacetate reagent 34.17 The a-hydroxylation of enolsilanes derived from P-dicarbonyl compounds has also been described, although in some cases direct oxidation of the P-dicarbonyl compound is feasible without enolsilane formation.18... 

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