Synthesis, experimental and theoretical NMR study of 2'-hydroxychalcones bearing a nitro substituent on their B ring

The synthesis of several 2'-hydroxynitrochalcones has been accomplished by an aldol reaction of equimolar amounts of the appropriate 2'-hydroxyacetophenones with nitrobenzaldehydes in alkaline medium. The reaction of 2'-hydroxyacetophenones bearing a 6'-methoxy with 2- or 4-nitrobenzaldehydes gave the expected 2'-hydroxynitrochalcones and also 4-methoxynitroaurones, being the latter ones the unique reaction products when using 2 molar equiv of nitrobenzaldehydes. The reaction mechanisms for the formation of both products are discussed. The C-13 NMR chemical shifts have been discussed first by means of an empirical additive model and then by comparison with GIAO/B3LYP calculated absolute shieldings. (C) 2004 Elsevier Ltd. All rights reserved.