5-[(2-Furyl)methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione (1a) treated with equimolar amount of pyrrolidine or hexahydroazepine afforded 5-(pyrrolidine)- (2a) or 5-[(hexahydro- azepine-1-yl)-2-hydroxypenta-2,4-dien-1-ylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione (2d). Their treatment with hydrobromic acid led to cyclization and formation of stable 5-cyclopentenyl-4H-1,3-dioxine hydrobromides (3a, 3d). Under the same conditions 1a treated with morpholine or piperidine yielded a mixture of 2b, 3b and 2c, 3c, respectively. The corresponding 3-substituted furans 1b-1e gave only substituted 5-cyclopentenyl-4H-1,3-dioxines (3e-3i). The use of an excess amine in reaction with 1a yielded unexpectedly 5-(3,5-dihetaryl-cyclopent-2-en-1-ylidene)-2,2-dimethyl-1,3-dioxane-4,6-diones (9a-9c) and 5-[5-hexahydroazepin-1-ium-1-ylidene-2-(hexahydroazepin-1-yl)cyclopent-1-en-1-yl]-2,2-dimethyl-4-oxo-4H-1,3-dioxin-6-olates (10).
5-[(2-呋喃基)甲基亚甲基]-2,2-二甲基-1,3-二氧杂环戊烷-4,6-二酮(1a)与吡咯或六氢吡嗪等量反应生成5-(吡咯基)-(2a)或5-[(六氢-吡嗪-1-基)-2-羟基戊-2,4-二烯-1-亚甲基]-2,2-二甲基-1,3-二氧杂环戊烷-4,6-二酮(2d)。它们与直溴酸处理后环化形成稳定的5-环戊烯基-4H-1,3-二氧杂环戊烷直溴酸酯(3a,3d)。在相同条件下,1a与吗啡或哌啶反应生成2b,3b和2c,3c的混合物。相应的3-取代呋喃类化合物1b-1e仅产生取代的5-环戊烯基-4H-1,3-二氧杂环戊烷(3e-3i)。在反应中使用过量胺与1a反应意外产生5-(3,5-二芳基-环戊-2-烯-1-亚甲基)-2,2-二甲基-1,3-二氧杂环戊烷-4,6-二酮(9a-9c)和5-[5-六氢吡嗪-1-基-2-(六氢吡嗪-1-基)环戊-1-烯-1-亚甲基]-2,2-二甲基-4-酮-4H-1,3-二氧杂环戊烷-6-醇酯(10)。