A series of 2,4-disubstituted 3,4-dihydro-2H-pyran-5-carboxaldehydes II-XIX was prepared by reaction of substituted arylmethylenemalonaldehydes I with 2-methylpropane, 1,1-diphenylethylene, styrene, ethyl vinyl ether, 1,1-dimethoxyethylene and 1,1-bis(methylthio)ethylene. In the case of the reaction with ethyl vinyl ether the dependence of the ratio of the arising cis- and trans- 2-ethoxy-4-aryl-3,4-dihydropyran-5-carboxaldehydes VII-XIV on the substitutent on the aromatic nucleus was studied. Information on the mechanism of this reaction was obtained and conformational equilibria of 2-ethoxy-4-aryl-3,4-dihydropyran-5-carboxaldehydes in solution were studied by 1H NMR spectroscopy. The structure of trans-2-ethoxy-4-(4-chlorophenyl)-3,4-dihydropyran-5-carboxaldehyde (trans-VIII) was confirmed by X-ray analysis of the corresponding carboxylic acid trans-XXII.
一系列2,4-二取代3,4-二氢-2H-吡喃-5-羰基醛II-XIX通过取代芳基亚甲基马隆醛I与2-甲基丙烷、1,1-二苯基乙烯、苯乙烯、乙基乙烯醚、1,1-二甲氧基乙烯和1,1-双(甲硫基)乙烯反应制备。在与乙基乙烯醚发生反应的情况下,研究了芳香核上取代基对产生的顺式和反式2-乙氧基-4-芳基-3,4-二氢吡喃-5-羰基醛VII-XIV的比率的依赖关系。通过1H核磁共振波谱研究了溶液中2-乙氧基-4-芳基-3,4-二氢吡喃-5-羰基醛的构象平衡,并获得了有关该反应机理的信息。通过对应羧酸的X-射线分析,确认了反式-2-乙氧基-4-(4-氯苯基)-3,4-二氢吡喃-5-羰基醛(反式-VIII)的结构。