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46413-B1
The Synthesis of Novel Indenofluorenes

William A. Feld, Wright State University

Carboxylated cyclopentadienones (CCPD) react readily in Diels Alder reactions with inverse electron demand (dienophile is electron rich). They present many intriguing possibilities. The functionalization provided by the dienophile (propargyl derivatives) in Diels-Alder reactions with the carboxylated cyclopentadienone (CCPD), 2, 5-dicarboethoxy-3,4-diphenylcyclopentadienone 1 has been initially investigated.

The synthesis of 1 follows an Aldol condensation pathway that employs diethyl (or dimethyl) acetonedicarboxylate 2 and benzil 3. The unsubstituted CCPD 1 (X = H) has been dubbed "Orange" because of its color and has generally been the basis for preliminary research and continues to be a versatile starting material for many applications. The synthesis of 1 has recently been carried out on 50 g scale and its purification (recrystallization vs chromatography) has been improved.

The current reactions of CCPDs are centered on the Diels Alder reaction with the propargyl systems propargyl acetate 4, propargyl chloride 5, propargyl bromide 6, propargyl ether 7, dimethyl acetylenedicarboxylate 8 and trispropargyl amine 9.

The reaction of 1 and propargyl acetate 4 provided diethyl 2,3-diphenyl-5-acetoxymethylterephthalate 10. The acetate could be characterized by ¹H NMR absorptions and integrations for the acetate methyl (2.13 d), the benzylic methylene (5.27 d), the ethyl ester methyl (0.89 d) and methylene (3.98 d) and appropriate aromatic absorptions, especially the singlet (7.86 d).

The acetate 10 was intramolecularly transesterified with sulfuric acid to generate a 50/50 (by ¹H NMR) mixture the lactone 11 and the starting material 10. Characterization of 11 was based on the lactone singlet (5.38 d).

The reaction of propargyl chloride 5 and 1 produced diethyl 2,3-diphenyl-5-chloromethylterephthalate 12. Characterization of 12 followed that associated with 11. The ¹H NMR absorption and relative integration of the benzylic methylene (4.77 d) of the chloromethyl substituent clearly distinguishes 11.

The reaction of propargyl bromide 6 with 1 cleanly provided the bromomethyl derivative, diethyl 2,3-diphenyl-5-chloromethylterephthalate 13. The characterization of 13 was not, however, straightforward. The crude product exhibited the expected ¹H NMR absorptions and integrations but after recrystallization from ethanol, a 75% recovered yield of 11 was obtained. Furthur investigation of the lactone formation is underway.

The use of propargyl ether 7 as a Diels-Alder reactant with 1 was investigated from two positions. Initially, a calculation error in the ratio of 7 to 1 (10:1 was used instead of 1:1) produced the monoreacted propargyl substituted terephthalate 14. The characterization of 14 by ¹H NMR was based on the appearance of an absorption for the benzylic methylene (3.99 d) and the propargylic methylene (4.06 d) as well as the terminalm alkyne proton (2.19 d) in addition to the related terephthalate absorptions..

This error had the unintended consequence of providing an entry into a series of compounds containing pendent ethynyl units, a process usually associated with protection-deprotection schemes. It appears that this can be a preparative method as long as the boiling point of the diyne is not excessive.

The reaction of 7 and 1 in a 1:2 ratio provided the bisterephthalate 15. The usual characterization was used to establish the absence of a pendent propargyl unit in the structure.

A preliminary probe of the suitability of the polyterephthalates for conversion to the corresponding indenofluorenones was conducted using 15. The hydrolysis of 15 was carried out to yield the tetraacid 16. It could be established that the benzylic ether bridge between the terephthalate moieties was intact. Furthur studies on this system (intramolecular ring closure) are underway.

The reaction of dimethyl acetylenedicarboxylate 8 with 1 was undertaken to provide access to a polysubstituted product with wide potential. The characterization of 17 was easily established by ¹H NMR. Appropriate ethyl ester and methyl ester absorptions and integrations were observed.

An entry into the polysubstituted terephthalate systems was established by the reaction of 9 with 1. The reaction was staged (80°/24h, 120°/24h) to prevent the loss of the volatile 9. Future reactions involving 9 will be conducted in closed systems. The characterization of the congested triterephthalate 18 was based on surprisingly clear ¹H NMR absorptions and integrations for the benzylic amine methylenes (3.85 d), the ester methylenes (4.01 d), the ester methyls (0.88 d), and in particular the singlet associated with the lone proton on the terephthalate ring (8.11 d).

The reactions outlined in this report set the stage for the investigation of 1) additional CCPD substitution by way of substituted benzils, 2) the use of polypropargyl substrates in the preparation of polyterephthalates and 3) the manipulation of polyterephthalic acids as precursors to polyindenofluorenones.