Sulfuric Acid → 6,7-Dihydro-2-methyl-5-methylenebenzo(b)furan-4(5H)-one

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To a solution of conc. H2SO4 (300 ml) cooled in an ice-bath was added a solution of 3-hydroxy-2-(2-oxopropyl)-2-cyclohexen-1-one (190 g in 300 ml CH2Cl2). Upon completion of addition, the mixture was stirred at ambient temperature for about 1 hour. The mixture was then slowly poured into 3 liters ice water, and then about 1 liter of CH2Cl2 was added. The layers are separated and the aqueous layer extracted thrice with CH2Cl2 and the combined CH2Cl2 layers again extracted thrice with water. The CH2Cl2 layer was washed thrice with dilute aqueous NaHCo3, then once with water and dried (MgSO4). Concentration in vacuo afforded an orange oil. Step B. To a solution of the furanone of Step A (164.5 g, 1.10 mole) in about 400 ml THF was added, in four separate portions, N-methylanilinium trifluoroacetate (TAMA) (243 g) and trioxymethylene (99 g) over 3-1/2 hours, and the mixture refluxed for 20 hours. The mixture was cooled and partitioned between Et2O and water, the layers separated and the aqueous layer was extracted twice with Et2O. The combined Et2O layers were washed exhaustively with water, with NaHCO3 and then with brine, dried over MgSO4 and conc. in vacuo to yield an amber oil. This oil was flash chromatographed on silica gel using CH2Cl2 as solvent in several runs of 10-20 g per run. Fractions containing the fast moving material were combined, concentrated in vacuo to obtain the desired product as a yellow oil.

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