One-Pot and Chemoselective Synthesis of Alkyl 2-Oxo-2H-Benzo[h]Chromene-4-Carboxylates Derivatives Catalyzed by Nano Silica Powder

While chromene skeleton compounds have been long studiedin recent years they have attracted a greater growing interest, some having been found to possess properties of considerable pharmacological or industrial significance[1,2]. In this article, we report on the catalytic activity of nano silica powder in the conversion of dialkyl 2-(1- hydroxy-2-naphthyl)-3-(triphenylphosphoranylidene)butanedioates to alkyl 2-oxo-2H-benzo[h]chromene-4-carboxylates in solvent-free conditions at 60◦C in fairly good yields (Scheme 1). The ylide (5) may result from initial addition of triphenylphosphine 1 to the acetylenic ester 2 and concomitant protonation of the 1:1 adduct, followed by the electrophilic attack of the vinyltriphenylphosphonium cation on the aromatic ring at ortho β-position relative to the strong activating group (Scheme 1). TLC indicated formation of ylides 5 in CH2Cl2. Nano silica powder was found to catalyze conversion of ylides 5 to alkyl 2-oxo-2H-benzo[h]chromene-4-carboxylates (6) in solvent-free conditions at 60◦C in fairly good yields (Scheme 1). TLC indicated that the reaction was completed after 20 min.