Preparation of an a,b-Type of Ter- and Septithiophenes

w i t h a l o w -v a l e n t t i t a n i u m r e a g e n t .Thiophene oligomers continue t o a t t r a c t much attention because o f t h e i r unique biological a c t i v i t i e s 1 and also as starting materials for the preparation o f organic conductors.I n our continuing synthetic study on thiophene oligomers, we have previously reported the syntheses of a series of an a-type o f thiophene oligomers including o-ter-,2-4 a-quater-,5 u-quinque-,6 ~s e x i -, ~ a-septi-,6 and h -o ~t i t h i o p h e n e s .~ Herein we report the preparation o f an 0.6-type o f thiophene oligomers, t e r -and septithiophenes (4 and 12).--The synthetic strategy for 4 and 12 stems from our previous thiophene The reductive * -