The Synthesis of New Spirolactones from Substituted Isatins

Interaction of N-ethyl isatin 3 with dimethyl acetylenedicarboxylate in the presence triphenylphosphine has led to good selectivity of methyl 1'-ethyl-4-methoxy-2',5-dioxo-5H-spiro[furan-2,3'-indoline]-3-carboxylate 4 formation. Similar yields of spirolactones 6,8 were obtained by addition of dimethyl acetylenedicarboxylate to 5-bromo functionalized isatins 5,7. However, reaction of N-butyl isatin 9 resulted in formation of an inseparable mixture of compounds. Treatment of N-benzyl isatin 10 and dimethyl acetylenedicarboxylate with triphenylphosphine proceeded with reduced selectivity of the spirooxindole 11 formation.