Bound ketones

Stoichiometric ionic hydrogenation of the C=C bond of a,/ -unsaturated ketones by HOTf and [Cp(CO)3WH] results in the formation of -ketone complexes of tungsten [32]. As exemplified in Eq. (17), hydrogenation of methyl vinyl ketone gives a 2-butanone complex of tungsten. The bound ketone is displaced by the triflate counterion, giving the free ketone. Similar reactions were reported for hydrogenation of the C=C bond of a,/ -unsaturated aldehydes. 

Displacement of the bound ketone by H2 was directly observed by NMR (Eq. (37)), and an approximate equilibrium constant was determined. The cationic tungsten complex can also be used for catalytic hydrosilylation of ketones. In the case of catalytic hydrosilylation of abphatic substrates using HSiEt3, the catalyst precipitates at the end of the reaction, facilitating recycle and reuse [66],... 

Figure 6.23 Proposed transition states of the asymmetric 72-catalyzed cyanosilylation of ketones describe two alternative mechanistic pathways for cooperative catalysis Addition via thiourea-bound ketone (TS 1, preferred) and addition via thiourea-bound cyanide (TS 2).

A further type of linker, especially designed for facile nucleophilic cleavage, is the oxime linker. Oximes of resin-bound ketones or aldehydes can be acylated to yield O-acyl oximes, which are readily cleaved by a variety of nucleophiles (Table 3.14). A widely used support of this type is p-nitrobenzophenone oxime resin (Kaiser oxime... 

C-Acylations of C,H-acidic compounds have also been realized on insoluble supports. The few examples that have been reported include the C-acylation of support-bound ester enolates with acyl halides [9], Claisen condensations of polystyrene-bound ketones with benzoic acid esters, the C-acylation of nitriles with acyl nitriles or anhydrides, and the C-acylation of phosphonates with acyl halides (Entries 5-9, Table... 

Friedel-Crafts acylation with various acyl chlorides of resin-bound 3,4-dimethoxyphenylacetate afforded resin-bound ketones which, following treatment with hydrazine, were converted into the corresponding 2,3-benzodiaze-pines in good yields and purities <2001TL7683>. 

FIGURE 13 Et Et Horner-Wadsworth-Emmons reactions were performed with a polymer-support-bound ketone resembling the CD ring of vitamin D3. [207]... 

Cyclodextrins with two imidazole groups on the primary hydroxyl side can enhance the enolate formation [86] of a simple bound ketone by bifunctional acid-base catalysis and accelerating the intramolecular aldol condensation of bound ketoaldehyde and dialdehyde. The aldolase mimics which catalyzed crossed aldol condensations were obtained by the assembly of (i-CD and various amino moieties as Schiff base [87]. 

Oxone, MeCN-aq EDTA, rt polymer-bound ketone... 

The proposed mechanism for the catalytic hydrosilylation (Scheme 3.5) shares some similarities to that proposed for catalytic ionic hydrogenations (Scheme 3.4). Displacement of the bound ketone by HSiEts gives [CpW(CO)2(lMes)(SiEt3)H], which has been independently synthesized and characterized. Transfer of the... 

Cyclohepta-amylose has been converted into the phosphates (21)—(23), which were examined as catalysts for the hydrolysis of 4-nitrophenyl tetrahydropyranyl ether at low pH and for the exchange of 4-t-butylphenacyl alcohol (tritiated in the a-methylene group) at high pH. All three isomers, as the phosphate dianions, were effective catalysts for the latter reaction in which the functional group assists enolization of the bound ketone. Only the 3-phosphate (22) showed net catalysis of the hydrolysis of the ether, which was bound and hydrolysed with the assistance of a monoanionic phosphoric acid group. 

Radiochemical techniques (Percy, 1964 Houseman, 1970 Barnard et aiy 1972) would appear to provide the least objectionable approach to the study of scission reactions. For uncross-linked rubber it was found that one bound ketone group was formed per scission event. This figure was obtained by the use of C -dinitrophenylhydrazine which was used to measure bound (aldehyde + ketone) and C -dime-done which was used to measure bound aldehyde, the bound ketone being obtained by difference. 

Condensation of resin bound ketones with hydrazines followed by cyclizative cleavage was used in a synthesis of pyrazolinones [67]. Samarium iodide induced radical cyclization of allyl aryl ethers led to benzofuran derivatives [68]. Kurth et al. have reported a two reaction iterative process for the construction of polyisoxazolines [69] and polyisoxazoles [70]. An intramolecular Heck reaction has been employed to prepare 2-oxindole derivatives [71]. 

Synthesis of Vitamin D3 Core 248 Phosphine oxide 245 (1.1 equiv) was dissolved in anhydrous THF, cooled to —50°C, and treated with nBuLi (1.0 equiv) under argon. The mixture was then transferred via cannula to a solution of resin-bound ketone 244 (0.72 equiv) in anhydrous THF and reacted at —40°C to — 10°C for 3 hours to yield immobilized triene 246. Concomitant alkylation and cleavage from the polymer-support occurred via a copper-promoted Grignard reaction with 247 at room temperature for 3 hours. The crude protected product was then immediately treated with CSA in methanol and water at room temperature for 6 hours to afford vitamin D3 analog 248 in 47% yield (from 244). 

Wamser has studied the photochemistry of cyclohexylacetyl groups bonded by Friedel-Crafts acylation to polystyrene beads, which provides an a-cyclohexyl acetophenone structure. The polymer-bound ketone reacts with almost the same quantum efficiency as the free ketone in pentane, 50%, but is unreactive in ethanol, which does not swell the polymer and allow the molecular motion necessary for reaction. 

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