Hetero-Diels-Alder reaction of propenenitriles with enol ethers:a convenient approach to functionalized 3,4-dihydro-2H-pyrans

摘要

The hetem-Diels-Alder reaction of 3-(N-acetyl-N-benzylamino)-2-formylprop-2-enenitrile with enol ethers yielded cis/trans diastereoisomers of 2-alkoxy-4-amino-3,4-dihydro-2H-pyran-5-carbo-nitriles in moderate yields.Acidic hydrolysis of cis-diastereoisomer in concentrated sulfuric acid gave 2-oxo-l,2-dihydropyrydine-3-carbaldehyde.The reaction of 2-benzoyl-3-heteroaromaticprop-2-eneni-triles with enol ethers afforded diastereoisomeric cis/trans cycloadducts in good yields.The structure of the products is discussed in terms of configuration and preferred conformation.