cycloadditions of 4-substituted methyl 2-oxo-3-butenoates and -3-pentenoates with alkenes took place with high regio- and stereoselectivities to afford substituted 6-methoxycarbonyl-3,4-dihydro-2H-pyrans in good to moderate yields. None of the ene products were produced. Similar reactions of methyl 3-phenyl-2-oxo-3-butenoate with alkenes afforded both the corresponding 3,4-dihydro-2H-pyrans and a dimeric cycloadduct
路易斯酸催化 4-取代的 2-氧代-
3-丁烯酸甲酯和-
3-戊烯酸甲酯与烯烃的环加成反应具有高区域选择性和立体选择性,得到良好的取代 6-甲氧羰基-
3,4-二氢-2H-吡喃到适度的产量。没有生产烯产品。3-苯基-2-氧代-
3-丁烯酸甲酯与烯烃的类似反应得到相应的
3,4-二氢-2H-吡喃和二烯组分的二聚环加合物。目前的逆电子需求环加成反应的区域选择性和立体选择性表明反应是通过协调一致的外向过渡态进行的。