2-ADDITION OF PYRROLES TO DIMETHYL ACETYLENEDICARBOXYLATE - MICHAEL-TYPE ADDUCTS AND DIELS-ALDER PRODUCTS
2-ADDITION OF PYRROLES TO DIMETHYL ACETYLENEDICARBOXYLATE - MICHAEL-TYPE ADDUCTS AND DIELS-ALDER PRODUCTS
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DOI：
10.1021/jo01311a004
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发表时间：
1980-01-01
影响因子：
3.6
通讯作者：
LEE, CK
中科院分区：
文献类型：
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作者：
NOLAND, WE;LEE, CK
具有开放2位的吡咯1在活性氢源的存在下与乙酰二甲酸二甲酯(DMAD)反应，在本例中，活性氢源通常由它们自己的NH基团(如果存在)或由足够的醋酸提供，以在2位(2-吡咯基-2-丁二酸二甲酯)生成1：1的Michael类型的加合物，通常作为Z(3)和E(4)异构体。与所获得的数据类似，允许将立体化学指认给以前报道的其他几个1：1加合物，包括来自2，3-二甲基吡咯(LG)的3G和4G以及来自2，3，4-三甲基吡咯(LH)的3H。根据核磁共振和质谱学数据，将IF和DMAD的2：1加合物(3f和4f的副产物)重新命名为结构2，2-二(3，5-二甲基-2-吡咯基)丁二酸二甲酯(9)。3和4的形成通常与Diels-Alder反应竞争，在Diels-Alder反应中，吡咯充当二烯。与回流乙醚相比，Diels-Alder反应在没有醋酸等弱酸的情况下以及在较高的温度下倾向于相对有利。最初的1：1 Diels-Alder加合物(5)是不稳定的，没有被分离。它们倾向于通过四条途径中的一条反应：(1)它们回复到3和4；(2)它们进一步与DMAD反应，得到类型6的1：2加合物(四甲基3a，7a-二氢吲哚-2，3，3a，4-四羧酸盐)；(3)在更高的温度(63-160℃)下，它们发生逆Diels-Alder裂解，得到相应的N-取代吡咯-3，4-二羧酸二甲酯(7)；(4)它们消除桥氮，从LP和LQ得到4-取代邻苯二甲酸二甲酯(14)或(通过5和7以及7与DMAD的进一步Diels-Alder反应)四甲苯-1，2，4，5-四羧酸酯(24)。类型6的1：2加合物在其二烯体系中与DMAD进一步发生Diels-Alder反应，生成5-取代三甲基-1，2，3-三羧酸三甲酯(16)和1-取代吡咯-2，3，4-三羧酸酯(17，类似于7)。在少数情况下，观察到2-乙烯基吡咯3和/或4在吲哚的Diels-Alder合成中充当二烯。
Pyrroles 1 having an open 2-position react with dimethyl acetylenedicarboxylate (DMAD) in the presence of a source of active hydrogen, usually provided in the present cases by their own NH groups (if present) or by sufficient acetic acid, to give 1: 1 Michael-type adducts at the 2-position (dimethyl 2-pyrrolyl-2-butenedioates), usually as both the Z (3) and E (4) isomers. Analogy with thedata obtained permits assignment of stereochemistry to several other 1: 1 adducts previously reported, including 3g and 4g from 2, 3-dimethylpyrrole (lg) and 3h from 2, 3, 4-trimethylpyrrole (lh). On the basis of NMR and mass spectral data, the 2: 1 adduct of If and DMAD (a coproduct of 3f and 4f) is reassigned the structuredimethyl 2, 2-bis (3, 5-dimethyl-2-pyrrolyl) butanedioate (9). Formation of 3 and 4 is usually competitive with Diels-Alder reactions in which the pyrrole acts as a diene. The Diels-Alder reactiontends to be relatively favored in the absence of weak acids such as acetic acid and at higher temperatures than in refluxing ether. The initial 1: 1 Diels-Alder adducts (5) are unstable and were not isolated. They tend to react by one of fourpathways:(1) they revert to 3 and 4;(2) they react further with DMAD, giving 1: 2 adducts of type 6 (tetramethyl 3a, 7a-dihydroindole-2, 3, 3a, 4-tetracarboxylates);(3) at higher temperatures (63-160 C) they undergo retro-Diels-Alder cleavage, giving the corresponding dimethyl N-substituted pyrrole-3, 4-dicarboxylates (7);(4) they eliminate the bridging nitrogen to give dimethyl 4-substituted phthalates (14) or to give (via 5 and 7 and a further Diels-Alder reaction of 7 with DMAD) tetramethyl benzene-1, 2, 4, 5-tetracarboxylate (24) from lp and lq. The 1: 2 adducts of type 6 undergo further Diels-Alder reaction at their diene system with DMAD to give as coproducts trimethyl 5-substitutedbenzene-1, 2, 3-tricarboxylates (16) and trimethyl 1-substituted pyrrole-2, 3, 4-tricarboxylates (17, similar to 7). In a few instances the 2-vinylpyrroles 3 and/or 4 were observed to act as dienes in a Diels-Alder synthesis of indoles.