@article{2960843,
    title = "Synthesis of methylene-bridged polycyclic aromatic hydrocarbons: an efficient, double Friedel-Crafts cyclization approach to 11H-benz[bc]aceanthrylene",
    author = "Thanasis Gimisis and Jeff W. Kampf and Masato Koreeda",
    journal = "The Journal of Organic Chemistry",
    year = "1993",
    volume = "58",
    number = "21",
    pages = "5858--5861",
    publisher = "American Chemical Society (ACS)",
    doi = "10.1021/jo00073a058",
    abstract = "A five-step synthesis of 3-methylcholanthrene (1) has been achieved starting from 5-methylhomophthalic anhydride and N,N-diethyl-1-naphthamide in 55% overall yield. Treatment of a solution of the preformed lithium enolate of 5-methylhomophthalic anhydride (3) with an equimolar solution of 2-lithio-1-naphthamide (4), followed by acid hydrolysis, provides cleanly the spirobislactone 5 in 80% overall yield. In addition, the synthesis features a unique, highly selective double Friedel-Crafts cyclization of the aryl diacid 2 with PPA to give rise, after acetylation, to keto acetate 6.  1993 America Chemical Society."
}