Highly Regioselective Tandem Reaction of Ene-Yne-Oxazolones Induced by H-Phosphonates: Construction of Phosphinylindane Derivatives

Abstract

A highly regioselective divergent approach for the phosphine-containing indane/indene derivatives from the ene-yneoxazolone precursors was reported. An insight into the reaction mechanism involving the phospha-1,4-addition followed by 5-exodig ring closure with a concomitant C−P/C−C bond formation was also proposed. This promising protocol utilized Hphosphonate as the phosphonating reagent in a silver-catalyzed or base-mediated cascade cyclization to construct the corresponding phosphorylated spiroindenoxazolones and amidoindenes, respectively, in good yields (up to 88% yield).

Base-Mediated and Silver-Catalyzed Divergent Synthesis of Hydroxynaphthalenamides and Phosphorylated Dihydronaphthylamides from Enone-Oxazolones

“…Additionally, 4 Å molecular sieves (4 Å MS) may affect the acidity of H -phosphonate and thus facilitate the electron transfer during the reaction to generate the phosphoryl radical for this phosphorylation/cyclization reaction sequence; this could be demonstrated when 1t furnished the desired product 3t in 75% yield (Scheme d). , Increasing the amount of water into the standard reaction as a mixture solvent, toluene:water in ratio of 1:1, was then performed, and the formation of 3a in 71% yield was observed (Scheme e). On the basis of these results and previous reports, , 4 Å MS can also act as a cocatalyst and catalyst support; the surface of the 4 Å MS could activate the O–H bond of water. In the absence of silver catalyst and the 4 Å MS, the reaction was performed with azobis­(isobutyronitrile) (AIBN) and yielded 3a in 78% yield (Scheme f).…”

“…Recently, we disclosed the phospha-1,4-addition followed by 5-exo-dig ring closure with a concomitant C–P/C–C bond formation of ene-yne-oxazolone with H -phosphonate as the phosphonating reagent in a silver-catalyzed to afford phosphorylated spiroindenoxazolones in good yield (up to 86%) . This strategy was subsequently employed to synthesize the phosphorylated dihydronaphthylamides 3 via phospha-1,4-addition/intramolecular cyclization of enone-oxazolones 1 with H -phosphonate (diphenylphosphine oxide, DPPO).…”

“…From our previous work, azlactone analogs could be transformed to some highly functionalized molecules such as tricyclic imidazoloisoquinolin-3-ones, benzo­[ a ]­quinolizin-4-ones, bicyclic 2,3-dihydrobenzo­[ d ]­azocin-4-ones, 3-amidocoumarins, 3-amidoazacoumarins, and phosphine-containing indane/indene derivatives . To the best of our knowledge, there has been no reported synthetic approach to hydroxynaphthalenamides or dihydronaphthylamides employing azlactones as starting materials.…”