Furans and thiophenes from etacrynic acid

Article abstract of DOI:10.1002/ardp.19923250104

The 1,4-dicarbonyl- and 1,4,7-tricarbonyl compounds 1 react with polyphosphoric acid (PPA) to yield the furans 3; with P₄S₁₀ the thiophenes 4 are obtained. The γ-keto carboxylic acid 2 cyclizes with PPA to form the α,β-unsaturated butyrolactone 6. 2 is reduced by NaBH₄ chemo- and diastereoselectively to give the γ-hydroxy carboxylic acid 5. The lactone 7 is prepared by dehydration of 5 with PPA. The sulfones 8a,b are obtained from the thiophenes 4a,b by oxidation with magnesium monoperoxyphthalate (MMPP). Under the same conditions the furan 3b is cleaved to yield the enedione 9, which tautomerizes slowly forming 10.