呋喃與丙二醯胺之分子內Diels-Alder反應

Abstract

以呋喃為二烯基、以丙二烯胺基作為親二烯基進行分子內Diels- Alder反應。將化合物3、18、31、40溶於第三丁醇中，以第三丁醇鉀作為鹼，於室溫下反應二十四小時可以得到開環後的產物5、22、33、44。 當Diels-Alder反應形成五角環時，由於環張力的影響，誘使氮原子上的未鍵結電子對朝β碳位置共振，最後共振電子對被氧原子所捕捉形成一開環結構。而當Diels-Alder反應形成六角環時由於環張力較小不易形成開環結構而以環加成產物為主，如化合物10、38。 此外，由於合成產物含有部分吡咯的結構，芳香環的性質使吡咯成為一理想的離去基，造成醯胺鍵易於親核反應下斷裂。因此可以得到化合物24、45。

We studied the intramolecular Diels-Alder reaction of furfuryl as diene with allenylamine as dienophile. Started with compound 3、18、31、40 solved in tert-butyl alcohol, potassium tert-butoxide as base, carried out at room temperature and proceeded twenty-four hours, then the ring opening product 5、22、33、44 should be obtained。 The ring strain caused by the five-membered ring formed from Diels-Alder reaction induced the non-bonding electron pair on nitrogen atom to conjugate toward β position. One conjugated electron pair catched by the oxygen atom resulted in the ring opening structure. However, the ring strain of six-membered ring is not sufficient for delocalization of the electrons on nitrogen, thus resulted in the predominated cycloadduct 10、38 。 Furthermore, we found that the aromatic pyrrole ring, one component of the product structure, behaved as a good leaving group under nucleophilic attack. Cleavage of the amind bond, product 24、45 ,was observed.