Serendipitous stereoselective synthesis of brand-new fluorescent dyes: (1Z)-3-(alkylimino)-1-[(chromone-3-yl)methylene]-1,3-dihydro-9H-furo[3,4-b]chromen-9-one-type fluorophores with blue fluorescence emission properties

The reactions of 3-formylchromones with alkyl isocyanides in dry dichloromethane at room temperature lead to new types of organic fluorophores (1Z)-3-(alkylimino)-1-(chromone-3-yl)methylene]-1,3-dihydro-9H-furo3,4-b]chromen-9-one, which exhibited strong blue emission in solution. The reactions involve a 4+1] cycloaddition followed by an activated electrophilic aromatic substitution at the furan ring and dehydration sequence.