Indeno fluorene-5,8-diones

The synthetic route utihzing Friedel-Crafts acylation via terphenyldicarboxylic acid precursors to reach the pentacycUc diketone has been applied for the assembly of a multitude of indeno[l,2-a]fluorene diones [44], In most cases, a mixture of [1,2-a] and [2,1-h] species was formed during the cychzation stage, although in some instances the [1,2-a] isomer was the exclusive product. One such example involves tricarboxylic acid precursor 36, so that the acylation step forms in the correct configuration regardless of direction (Scheme 9) [45]. To achieve this, cf5 -l,3-diphenylpropene (37) was reacted with 3-pentanone (38) to yield... 

The first account of the indeno[2,l-a]fluorene core in the literature dates to 1939 when Weizmann investigated polycyclic structures and their potential carcinogenic properties [23]. Intramolecular Friedel-Crafts acylation of 3,6-diphenylphthalic anhydride (113) in refluxing CS2 afforded fluorenone carboxylic acid 114 (Scheme 33). Acid chloride formation and subsequent cyclization in concentrated sulfuric acid generated the parent indeno[2,l-a]fluorene dione 115 in 5% yield with respect to 113. This was reaffirmed by Deuschel in 1951 where 115 is obtained in 72% under the same conditions [26]. 

Scheme 37 Original preparation of parent indeno [2,l-i)]fluorene dione 17 [26]...

The first account of 10,12-indeno[2,l-h]fluorene dione 17 dates to 1951 when Deuschel condensed phenylbenzoylacetylene (125) with ketodiester 126 to afford wt-terphenyl diester 127 (Scheme 37) [26], Saponification of 127 to 128 and subsequent ring closure yielded 11-hydroxy-[2, l-h]IF dione 129. Reduction using Zn metal provided 10,12-dihydro [2,l-h]IF 100. A final oxidation with sodium dichromate gave dione 17. 

An alternative method to Friedel-Crafts acylation as the final step in dione synthesis involves a Pd-mediated Heck arylation to generate the indeno[l,2-h] fluorene skeleton. In 1989, HeUwinkel and Kistenmacher showed that parent and 2,8-di -tert-butyl[l,2-b]lF diones 22 and 78, respectively, could be isolated upon reacting precursors 77a,b with palladium acetate in acetic acid (Scheme 18) [56,57]. 

Currently, only one example of a fully-conjugated indeno[2,l- ]fluorene is known and its existence at this time remains unofficial (Shimizu and Tobe, 2011, private communication). Tobe et al. synthesized the molecule in a near identical manner in which 115 was made - IF dione 17 was reacted with 2 equiv. mesitylmagnesium bromide to form diastereomeric diols 133. Further reaction with SnCl2 in the presence of trifluoroacetic acid yielded 10,12-dimesitylindeno [2,l-6]fluorene 134 (Scheme 39). Little is known about this molecule in terms of optoelectronic or stmctural properties. Due to the presence of the two s-cis diene linkages, however, 134 is considerably less stable than its [1,2-b] and [1,2-a] counterparts. 

Double ring closure. Powdered l-p-chlorophenyI-4-phenylnaphthalene-2,3-dicar-boxylic anhydride added at 100° to a molten mixture of AlClg and NaCl, the temp, raised to 140° during 15 min., and kept there for 2 hrs. 11-chloro-benz[c]indeno[2,l-a]fluorene-13,14-dione. Y ca. 100%. F. e. s., also single ring closure to ketocarboxylic acids (s. Synth. Meth. 8, 903), s. W. I. Awad et al., Soc. (C) 1971, 3721. 

Haley and coworkers simplified and expanded the scope of available fully conjugated indeno[l,2-fe]fluorenes in a subsequent report (Scheme 2.20) [69]. Easily accessible indeno[l,2-fe]fluorene-6,12-diones 33 were prepared in three steps. Then, addition of (triisopropylsilyl)ethynyllithium and an acidic work-up provides the diols. Reduction with SnCl2 in toluene yields fully conjugated derivatives of 28. The compounds were shown to reversibly accept two electrons... 

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