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had the idea last night that you could probably get anthrone (that's 9,10-dihydro-9-oxoanthracene) from natural materials, and get that to self-condense, with a Knoevenagel-type condensation between the keto group and the benzylic carbon
this paper seems to indicate feasibility
https://www.sciencedirect.com/science/article/pii/0032386178901003
also considering xanthone as a building block? you can get that from salicylic acid, with a bit of foolery. might be a route to interesting polymers