Abstract
Conjugate addition of nitroalkanes to 2H-chromene-3-carbaldehydes has been studied using a number of amines as the catalysts. Prolinol triethylsilyl ether was found to be the best catalyst for the reaction. The use of protonic solvents was also important. The reaction of variously substituted 2H-chromene-3-carbaldehydes with nitromethane afforded the products with excellent yields and diastereoselectivities. Nitroethane and 1-nitropropane were also applicable, however in decreased yields. The enantioselectivities of the reaction were very low and almost racemic products (3~5% ee) were obtained in all cases. The reaction provides a new method for the preparation of highly functionalized chroman derivatives.
Highlights
The chroman structural unit is found in a large number of drugs and natural products.[1]
We and Córdova et al found that the conjugate addition of bromonitroalkanes to α,βunsaturated aldehydes can be catalyzed by prolinol silyl ethers efficiently.[13]
Diphenylprolinol triethylsilyl ether was identified as the best catalyst for the reaction
Summary
The chroman structural unit is found in a large number of drugs and natural products.[1]. A number of achiral and chiral amines 1a-1l (Scheme 1) were examined as the catalysts for the reaction of 6-chloro-2H-chromene-3-carbaldehyde 2a and nitromethane.
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