Concise Synthesis of 3-Acetoxy-N,N-dialkylbenzo[b]thiophene-2-carboxamides from 2-Ethylsulfanylbenzoates

Abstract

A convenient method for the synthesis of 3-acetoxy-N,Ndialkylbenzo[b]thiophene-2-carboxamides has been developed in three steps from 2-ethylsulfanylbenzoates using an interrupted Pummerer reaction of N,N-dialkyl-3-(2-ethylsulfinylphenyl)-3-oxopropanamides. Thus, treatment of these sulfinyl amides, prepared by the reaction of 2-ethylsulfanylbenzoates with lithium enolates of N,N-dialkylacetamides followed by oxidation of the resulting N,Ndialkyl-3-(2-ethylsulfanylphenyl)-3-oxopropanamides with sodium metaperiodate and acetic anhydride at 100 °C leads to the formation of the desired benzo[b]thiophenes.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

“…Shortly after, the same group reported the use of an intramolecular 1,3-dicarbonyl tethered sulfoxide 124 in which cyclization through the enol form leads to benzothiophenes ( 125 ) after subsequent acylation at oxygen under the reaction conditions (Scheme 25b). 74…”

“…Herein, activation of the sulfoxide leads to an attack of the olefin on sulfur followed by deprotonation, with subsequent dealkylation affording the heterocycles. Shortly after, the same group reported the use of an intramolecular 1,3-dicarbonyl tethered sulfoxide 124 in which cyclization through the enol form leads to benzothiophenes ( 125 ) after subsequent acylation at oxygen under the reaction conditions (Scheme b) …”

“…Shortly after, the same group reported the use of an intramolecular 1,3-dicarbonyl tethered sulfoxide 124 in which cyclization through the enol form leads to benzothiophenes (125) after subsequent acylation at oxygen under the reaction conditions (Scheme 25b). 74 In 2015, Wan et al reported the use of an interrupted Pummerer reaction in the context of carbohydrate chemistry (Scheme 26). 75 Therein, sugar derivative 126 was introduced as a bench-stable glycosyl acceptor bearing a carefully disposed sulfoxide as a "remote silent activator", that could be switched on by the use of triflic anhydride (Scheme 26, bottom).…”