Synthesis of 3,4-Dihydro-2/f-pyrans by Hetero-Diels-Alder Reactions of Functionalized a,/?-Unsaturated Carbonyl Compounds with Styrenes
نویسنده
چکیده
H etero-Diels-Alder Reaction, a,/?-Unsaturated Ketones, Styrenes Cycloadditions of 3-aryl-2-benzoyl-2-propenenitriles la,b to styrene (2a) and its methylor methoxy-substituted derivatives 2b-d proceed regioand diastereoselectively yielding cis and trans diastereoisomers of 2,4,6-triaryl-3,4-dihydro-2//-pyran-5-carbonitriles 3 and 4 in 59-72% yield. Cycloadducts cis-3 were the major products. Reaction of 5-(4-nitrobenzylidene)-l,3-dimethylbarbituric acid (5) with styrenes 2a-d afforded diastereoisomeric mixtures of 2//-pyrano[2,3-d]pyrimidine-2,4(3//)-diones cis-6
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