Butyl esters interchange

Ester interchange. These clusters are mild but highly effective catalysts (e.g., in the preparation of t-butyl esters by reaction of methyl esters with f-butyl acetate, while removing methyl acetate continuously). They are kinetically less basic and therefore useful in dealing with enolizable esters. 

Treatment of 649 with ethanedithiol in the presence of boron trifluoride etherate results in acetal—thioacetal interchange at C-6 and subsequent lactonization of the 4)5-hydroxyl group with the r/-butyl ester, thus furnishing 651 in 83% yield. Reduction of the lactone to a lactol, protection with a MOM group, hydrolysis of the thioacetal, and reduction of the ketone with lithium aluminum hydride gives 653 as a single product. After benzoylation of the alcohol, conversion of the OMOM derivative to carboxamide (OMOM —> OAc CN — CONH2) affords 140 as a 10 1 mixture of isomers. 

Various esters of acrylic add are commercially available but methyl, ethyl and butyl acrylates are the most widely used. These esters are obtained by esterification of acrylic acid. The appropriate alcohol, acrylic acid and a catalyst (generally sulphuric add) are fed into a reactor at about 80°C and the ester separated by distillation. Higher acrylates are conveniently prepared by ester interchange. 

The sulfur analogue of the Hauser ortho-substitution rearrangement provides access to an arylacet-ic NSAID. Reaction of the aminobenzophenone 176 with ethyl methylthioacetate and tert-butyl hypochlorite gives the intermediate 178. The reaction probably proceeds by way of formation of the S-chlorinated sulfonium derivative 177 displacement on sulfur will lead to the salt 178. Treatment with triethylamine leads initially to the betaine 179. Electrocyelic rearrangement of that transient intermediate leads, after rearomatization, to the homoanthranilic acid 180. Internal ester-amine interchange leads then to indolone 181 [45]. The thiomethyl group is then removed with Raney niekel. Saponifieation of intermediate 182 affords bromfenac (183) [46J. 

Commercial amyl formate is an anhydrous, colorless liquid composed of a mixture of isomeric amyl formates with the isoamyl formate in predominance. This mixture is miscible with oils, hydrocarbons, alcohols, ketones and so forth. It is a solvent for cellulose esters, "Cumar , copal, gum esters, etc. It is able, when mixed with an alcohol, to dissolve shelloc and alkyd resin. It Is a less odoriferous and mare energetic solvent than amyl acetate. It also has bath a lower boiling point and a greater speed of evaporation. n-Butyl acetate and amyl formate have similar volatility and have substantially the same solvent power which permit free interchange of these only as far as these properties allow. 

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