REGIOSPECIFIC SYNTHESIS OF 3,4-DISUBSTITUTED FURANS .8. REGIOSPECIFICSYNTHESIS OF 3,4-DISUBSTITUTED FURANS AND 3-SUBSTITUTED FURANS USING 3,4-BIS(TRI-N-BUTYLSTANNYL)FURAN AND 3-(TRI-N-BUTYLSTANNYL)FURAN AS BUILDING-BLOCKS

Furan nucleus abounds in naturally occurring oxygen-containing compoun ds.(3) They are divided according to their structural features into fu ranosesquiterpenes, furanocembranolides and furanoid fatty acids, etc. Many of these furan natural products have interesting biological acti vities, such as cytotoxic and antitumor properties,(6,7) antispasmodic ,(8) antifeeding,(9) and several other potentially useful activities. More natural furan-containing compounds continue to be found at a rapi d pace.(10) In addition to being important building blocks found in na tural molecules with pharmaceutical implications, polysubstituted fura ns(11) appear also especially worthy of study because they can serve a s starting materials for the syntheses of natural and non-natural prod ucts.(12) Nevertheless, the tendency of furans to undergo both lithiat ion and electrophilic substitution at C-2 or C-5(13) makes the synthes is of 3,4-disubstituted furans an exceedingly challenging task. To eva de this, several special methods have been blueprinted.(14) We would l ike to report herein the preparation of 3,4-bis(tri-n-butylstannyl)fur an (1) and its pivotal role as a prominent building block for 3,4-disu bstituted furan. Recent works on the conversion of trialkylstannylfura ns(15) to 3-substituted furans also prompted us to disclose our own re sults on the preparation of similar compounds utilizing 3-(tri-n-butyl stannyl)furan (2), which was unexpectedly isolated as a side product i n our preparation of 1.