An easy and efficient method for the synthesis of 2,2-dialkyl-3-nitrochromene

Reactions of salicylaldehyde 1, 1,4-diazabicyclo[2.2.2]octane (DABCO), with β-nitrostyrenes 2, 4, 12, 14, and 16, respectively, in the absence of solvent at 40°C gave high yields of 3-nitro-chromenes. Only 96% of trans-3-nitro-4-hydroxyflavans 7 or 98% of 10 were isolated when compounds 6 or 9 reacted with 1 and DABCO under similar conditions. When the reaction temperature was increased to 90°C, 7 and 10 underwent dehydration to generate 74% of 8 and 89% of 11.