SYNTHESIS OF BIS-2,5-LINKED TETRAHYDROFURANS VIA IODOETHERIFICATION

Iodoetherification of alcohol 4 and several ether derivatives 12-15 afforded bis-tetrahydrofurans 8 and 9. The ratio of 8:9 depended on the nature of the ether substituent with 8 being the major product for R=H, SiMe(3), and Si(t)BuPh(2) whereas 9 was favoured when R=dichlorobenzyl. Attempts to effect ring expansion of 8 afforded ketone 16 wherein hydride migration had occurred. Iodoetherification of trisubstituted hydroxyalkene 17 afforded predominantly iodoether 21. Attempts to increase the amount of iodoether 22 formed led to a 1:1 ratio of 21:22 using trimethylsilyl ether 23. Treatment of iodoether 21 and 22 with Ag2CO3 in aqueous acetone proceeded stereospecifically affording the ring expansion products 27 and 28 respectively. Pyran 28 possesses the same stereochemistry as that present in the polyeher antibiotic salinomycin.