New aspects in the synthesis of mono- and dialkylfurans

Article abstract of DOI:10.1016/S0040-4020(01)86685-0

3-substituted furan systems can be obtained by alkylation of 3-lithium furans with various electrophiles in the presence of hexamethylphosphoric acid triamide in good yields. The 2- or 5-position of 3-methyl furan is blocked with high regio selectivity by silylation. After metalation and alkylation of the remaining free α-position and subsequent desilylation the 2,3- and 2,4-disubstituted furans are obtained. These methods are used to synthesize the naturally occuring compounds ursinanolide (2) and longifolin (4).