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 beta -nitrostyrenes 2, 4, 12, 14. and 16, respectively, in the absence of solvent at 40 degreesC 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 degreesC, 7 and 10 underwent dehydration t o generate 74% of 8 and 89% of 11. (C) 2001 Elsevier Science Ltd. All right s reserved.