Highly Functionalised Furans from 3-Bromochromone

3-Bromochromone reacts readily at room temperature with acetylacetone in chloroform in the presence of two equivalents of DBU. The product, isolated in 83% yield in the usual manner after quenching of the reaction mixture with 5% HC1, is 3-acetyl-5-(2-hydroxybenzoyl)-2-methylfuran. A variety of (3-diketones and P-keto esters react similarly to give moderate to excellent yields of highly functionalised trisubstituted furans. 

Explain this novel synthesis in mechanistic terms. 

Annulation of a benzene derivative to the naphthalene framework normally requires a number of steps. A recent one-pot procedure involves heating the benzhydrols 1 in toluene with a five-fold excess of maleic anhydride for several hours, and gives the 1-arylnaphthalene derivatives 2 in moderate yield. 

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