Thiophen Analogues of Fluorene

Thiophen Analogues of Fluorene.— During recent years several groups have been interested in the synthesis and chemistry of thiophen analogues of fluorene. MacDowell and co-workers have now synthesized the remaining two monothiophen analogues (456) and (457). The former compotmd was 

The effect of the mode of annelation on the acidity of the fluorenic hydrogens is clearly noticeable. (456) is metalated by butyl-lithium only at the 4-position, whereas (457) gives upon metalation and carbonation a mixture consisting of 38% of the 8-acid, 14% of the 1-acid, and 48% of the 3-acid of (457). 26c Treatment of 3-thienylmandelic acid (460) with Aids in benzene gave the 4-acid of (456). A similar ring-closure to (461) was obtained upon treatment of methyl 3,3 -dithienylglycolIate with chlorosulphonic acid in methylene chloride.  

The nitration of (462) yields 10% of the 6-nitro-derivative and 30% of a mixture of the 2-nitro- and 2,6-dinitro-derivatives. Two alternative routes to (463) starting from (464) have been described. A very interesting synthetic route to the fluorene analogue series was found in the reaction of 

AlCla-catalysed ring-closure of the acid chlorides of 3-phenylbenzo[6]thio-phen-2-carboxylic acid and 2-phenylbenzo[h]thiophen-3-carboxylic acid, respectively. Interestingly, direct ring-closure of 3-phenylbenzo[h]thio-phen-2-carboxylic acid with PPA yields (470). The reaction proceeds most 

Wynberg and co-workers have previously prepared all six dithiophen analogues of fluorene. Recently all fluorenone analogues (471)—(476) 

---

The coupling of thienyl-lithium derivatives with cupric chloride to yield symmetrically substituted bithienyls has during recent years been extensively used in connection with work on optically active bithienyl derivatives and in connection with the synthesis of thiophen analogues of fluorene, " and dithienothiophens. " Thus 3,3 -bithienyl and 4,4 -dibromo-3,3 -bithienyl prepared in this way were brominated to form hexabromo-3,3 -bithienyl. Halogen-metal exchange occurred selectively in the 5,5 -positions, yielding the acid (93) upon carbonation. (93) was resolved into... 

---