Hetero-Diels-Alder cycloadditions of ?,?-unsaturated acyl cyanides. Part 2. Reactions withN,N-dimethyluracils, a new route to 5-substituted uracil derivatives
作者:Jin-Cong Zhuo、Hugo Wyler
DOI:10.1002/hlca.19930760510
日期:1993.8.11
various acids, esters, or amides, i.e. derivatives 8a–c and 15–c, respectively. The methyl esters 8a (X MeO, R H) and 15a (X MeO, R H) are also formed directly from the adducts 3 and 10, respectively, with acid or base catalysis in presence of MeOH. The cycloadducts 17a and 17c, resulting from the reaction of 1a and 1c with 16, respectively, have a Me group at the ring junction C(4a) and are stable. The
2-氧代丁-3-烯腈(1a),2-氧代戊-3-烯腈(1b)和4-氰基-4-氧代丁-2-烯酸乙酯(1c)的[4 + 2]环加成为1,3研究了-二甲基尿嘧啶(2),1,3、6-三甲基尿嘧啶(9)或1,3,5-三甲基尿嘧啶(16)。1a与2或9的反应分别导致双环加合物3和10。这些六氢顺式吡喃并嘧啶在酸性条件下发生开环反应,并在4和11时恢复,分别为包含2-羟基丁-2-烯腈作为侧链在C(5)的尿嘧啶系统。令人惊讶地稳定的烯醇分别缓慢地互变异构成相应的酰基氰化物6a和13a。反应图1b或1c的带2,并用9不能提供cycloadducts; 相反,尿嘧啶衍生物6b,c和13b,c分别出现,并在C(5)处带有α-氧代丁腈侧链。用亲核试剂裂解6a–c和13a–c中的酰基氰官能团会产生各种酸,酯或酰胺,即衍生物8a–c和15–c分别。甲酯8a(X MeO,RH)和15a(X MeO,RH)也分别由加合物3