One-Pot and Chemoselective Synthesis of Alkyl 3-Oxo-3H-Benzo[f]Chromene-1-Carboxylates Derivatives Catalyzed by Nano Silica Powder

Chromene skeleton compounds occupy an important place in therealm of natural and synthetic organic chemistry. They are used as anticoagulants, additives in food and cosmetics, and in the preparation of insecticides, optical brighteners, and dispersed fluorescent and laser dyes. In this article, we report on the catalytic activity of Nano Silica Powder in the conversion of dialkyl 2-(1-hydroxy-2-naphthyl)-3-(1,1,1-triphenyl-λ5 -phosphanylidene) succinates to alkyl 3-oxo-3H-benzo[f]chromene-1-carboxylates in solvent-free conditions at 50◦C in fairly good yields (Scheme 1). The ylide (5) may result from initial addition of triphenylphosphine 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 α-position relative to the strong activating group (Scheme 1). TLC indicated formation of ylides 5 in CH2Cl2 . Silica gel powder was found to catalyze conversion of ylides 5 to alkyl 3-oxo-3H-benzo[ f ]chromene-1-carboxylates (6a–b) in solvent free conditions at 50◦C in fairly good yields (Scheme 1). TLC indicated that the reaction was completed after 20 min.