Thiophene → 4,5-Dimethyl-4,5-dihydro-6H-cyclopenta[b]thiophen-6-one

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Reaction Steps

To polyphosphoric acid (prepared from 500 g of P4O10 and 340 g of 85% H3PO4) a mixture of 47.6 ml (50.0 g, 0.60 mol) of thiophene and 59.5 g (0.60 mol) of tiglic acid in 80 ml of CH2Cl2 was added over 2.5 h at 50° C. This mixture was stirred at this temperature for 2 h, and, then, immersed in 1 kg of ice. The product was extracted with 3×300 ml of methyl-tert-butyl ether. The combined extract was washed with the saturated aqueous solution of Na2CO3, dried over K2CO3, and evaporated to dryness. Fractional distillation gave a colorless oil, bp 96-98° C./2 mm Hg. Yield 89.3 g (90%). On the evidence of NMR spectroscopy, the product is a mixture of two diastereomers (ca. 3:1).

Provenance & Evidence