Polystyrene supports, ester enolate

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... 

Most solid-phase syntheses of pyrazoles are based on the cyclocondensation of hydrazines with suitable 1,3-dielectrophiles. The reported examples include the reaction of hydrazines with support-bound a,(3-unsaturated ketones, 1,3-diketones, 3-keto esters, a-(cyano)carbonyl compounds, and a, 3-unsaturated nitriles (Table 15.19). Pyrazoles have also been prepared from polystyrene-bound 3-(hydrazino)esters, which are generated by the addition of ester enolates to hydrazones (Entry 7, Table 15.19 see also Section 10.3). Benzopyrazoles can be prepared from support-bound hydra-zones using the reaction sequence outlined in Figure 15.11. Oxidation of a polystyrene-bound benzophenone hydrazone yields an a-(acyloxy)azo compound. Upon treatment with a Lewis acid, this intermediate is converted into a 1,2-diazaallyl cation,... 

The delayed trapping experiments of an ester enolate in 10% cross-linked polystyrene, a benzyne in 2% cross-linked polystyrene, and a glycine active ester in 4% cross-linked polystyrene all gave lifetimes of about 1-10 minutes. Site isolation syntheses in tiie most common solvent-swollen polystyrene supports can be achieved if the reactive species is trapped quickly. More highly cross-Unked supports and poorly swelling solvents may give longer lifetimes of reactive intermediates, but no data are available. 

Chagl981 Chang, Y.H. and Ford, W.T., Use of Highly Cross-Linked Polystyrene Supports for Acylation and Alkylation of an Ester Enolate at Room Temperature, J. Org. Chem., 46 (1981) 5364-5371. 

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