Attempts to prepare an all-carbon indigoid system

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Materials Science

Background:

• Indigo, a vital dye, has a complex structure.
• Developing all-carbon analogs could lead to novel materials with unique properties.
• Previous synthetic routes to related compounds have limitations.

Purpose of the Study:

• To investigate the synthesis of a tetracyclic triene precursor for an all-carbon analog of indigo.
• To explore novel synthetic methodologies for constructing complex polycyclic carbon frameworks.
• To overcome challenges in preparing specific carbon-rich organic molecules.

Main Methods:

• Synthesis of α-methylene ketone 13 from indan-2-one (9).
• McMurry coupling of ketone 13 to yield bis-indene derivative 17.
• Dimerization of indan-1-one (18) to conjugated enedione 21 and bis-1-indene dimer 19.
• Reactions involving Tebbe reagent and alkylation with 1,2-dibromoethane.

Main Results:

• McMurry coupling of 13 yielded dimer 17, not the desired tetramethyl derivative of 4 (hydrocarbon 14).
• Methylenation of enedione 21 was unsuccessful.
• Tebbe reagent treatment of 19 led to dimer 23, likely via Cope rearrangement.
• Alkylation of 23 produced a mixture of spiro compounds 24 and 25.
• Reductive dimerization of 9 to 30 was achieved, but conversion to 14 failed.

Conclusions:

• The explored synthetic routes were insufficient for preparing the target all-carbon indigo precursor.
• Specific reactions like McMurry coupling and Tebbe olefination yielded unexpected products or failed under tested conditions.
• Further research is needed to develop viable strategies for synthesizing this class of polycyclic carbon compounds.