Site-recognition of one of the two alkoxy carbonyl groups present in the dienophile for Diels–Alder reaction

Recognition of one alkoxy carbonyl group from the two in a molecule by a Lewis acid was investigated using 1a–e in the Diels–Alder reaction with diene 6. Combination of 1a and BF3·OEt2 provided the highest efficiency to afford 7a, thus showing evidence for the site-selective coordination of BF3·OEt2 to the MOM-oxy carbonyl group in 1a. Furthermore, the generality and high reactivity of this combination were confirmed with dienes 11–14.