Novel intramolecular reductive Carbon-carbon coupling during borohydride reduction of dispiro[naphthalene-1,2′2^{\prime}(1′1^{\prime}H)-naphtho[2,1-b]pyran-3′3^{\prime},1^{\prime}^{\prime}-naphthalene]-2(1H),2^{\prime}^{\prime}(1^{\prime}^{\prime}H)-dione and similar dispironaphthalenones

$NaBH_4$ reduction of the title compounds I $(R=H, Br, Me_3C, 1-methyl-1-cyclohexyl)$ gave the coupling products II, III and IV $(R1=Me, Et, Me_2CH)$