Synthetic studies towards (+)-Dihydroampullicin. Michael addition of N-Boc-2-(tert-butyldimethylsiloxy)-3-methyl-pyrrole to α-methylene lactones

The Michael addition of N-(tert-butoxycarbonyl)-2-(tert-butyldimethylsiloxy)-3-methyl-pyrrole (4) to several α-methylene lactones catalyzed by fluoride ions yielded the corresponding homologated products (26–30) with good yields. Application of this reaction to the sililoxy bicyclic lactone (5) allowed us to isolate the tricyclic lactone (26), a highly valuable intermediate in our synthetic strategy leading to the growth regulator (+)-Dihydroampullicin (1).