Dialkylation of Ethyl 4-(Het)aryl-3-oxobutanoates as a Route to 5-(2-Oxoethyl)cyclopentenones

An unexplored ability of the long-known chemical transformation, Borsche's cyclopentenone synthesis (the construction of a 1,4-diketone with subsequent base-induced cyclization), is reported. Double alkylation of ethyl 4-(het)aryl-3-oxobutanoates with 2-bromo-1-(het)arylethanones, with subsequent alkali treatment, provides access to cyclopentenones substituted with a 2-oxoethyl group at the 5-position. These products might serve as valuable synthons for heterocyclization, and this feature was demonstrated by synthesis of 4 H -cyclopenta[ b ]thiophene derivatives.