(1) 4-Methyl phenylglyoxal [synthesized from 4-methyl acetophenone¹ (Sigma Aldrich), 97%, 142433]

(2) Dibenzyl phosphite (Sigma Aldrich), 100%, D36607

(3) Anhydrous sodium sulfate (Rankem), 99%, S0410

(3) Toluene (Rankem), directly used without drying

(4) n-Hexane (SD Fine Chemicals Ltd), directly used without drying

(5) Ethyl acetate (SD Fine Chemicals Ltd), directly used without drying

Reaction vessel was charged with 4-methyl phenyl glyoxal  (77 mg, 0.46 mmol) and dibenzyl phosphite (111 µL, 0.506 mmol) in 2 ml of Toluene and fitted with a reflux condenser and the reaction mass was heated for 7-9 h at 80 ^oC. The progress of the reaction was monitored by TLC, after its completion, the reaction mass was cooled to room temperature and excess solvent was removed under reduced pressure. The reaction mass was extracted with ethyl acetate from its aqueous workup. The EtOAc extract was dried over anhydrous Na₂SO₄. The it was purified by column chromatography on silica gel (100-200 #) using hexane and ethyl acetate (97:3) as eluent to afford the corresponding product with 75% yield at 90% purity.

• Due to 2-oxo group, the assistance of H-bonding, the dialkyl H-phosphonate form shifts towards more nucleophilic phosphite form.
• The phosphite group  later attacks 4-methyl phenyl glyoxal and generates the desired product and on heating in toluene loses one proton that generates a resonance stabilized caranion.
• This carbanions later attacks on molecular oxygen, and that rearranges to dioxaphosphetane intermediate and releases alkoxy nucleophile. 
• Under in situ acidic environment the dioxaphosphetane undergoes nucleophilic displacement reaction through elimination of H₂O and PO₃R molecules.

¹H NMR: (400 MHz, CDCl₃) δ 7.78 (d, J = 7.9 Hz, 2H), 7.41-7.26 (m, 5H), 7.20 (d, J = 7.9 Hz, 2H), 5.33 (s, 2H), 2.35 (s, 3H)

¹³C NMR:(126 MHz, CDCl₃) δ 185.77, 163.88, 146.39, 134.61, 130.21, 129.96, 129.68, 128.93, 128.82, 128.77, 128.64, 67.71, 21.98

IR (CHCl₃, cm^-1) ν 2922, 2852, 1737, 1681, 1303, 1169, 999, 696.

Battula, S.; Battini, N.; Singh, D.; Ahmed, Q. N., 2-Oxo Promoted Hydrophosphonylation & Aerobic Intramolecular Nucleophilic Displacement Reaction. Org. Biomol. Chem. 2015, 13, 8637-8641.

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