ChemInform Abstract: ON THE USE OF N,N′‐DIPYRROLYLMETHANE IN HETEROCYCLIC SYNTHESIS. DIPYRROLO(1,2‐C:2′,1′‐E)‐2H‐IMIDAZOLE AND ITS AROMATIC ANION

Abstract

SummaryThe pyrrolate ion (5) is shown to produce N, N'-dipyrrolyl methane (4) when reacted with dichloromethane under conditions of weak counter-ion association. 1 -Azoniafulvene ion (13) is suggested to be the key intermediate in this reaction. N , N'-Dipyrrolyl methane (4) undergoes intramolecular oxidative coupling when treated with butyllithium and Cu (II)chloride, yielding the novel ring system of dipyrrolo [ 1,2 c: 2', l'el-2 H-imidazole (3). The latter upon reaction with methyl lithium forms the Hiickel-aromatic anion 2. Solutions of the lithium salt are stable for several days. Reaction of the dianion of 2,2'-bipyrrole (11) with dichloromethane does not produce 3, but a pyrrolophane-type dimer (12) having its two anticoplanar N , N'-bipyrrolediyl subunits arranged in a double layer and joined by a methylene group on each side.Recent publications from our laboratory have discussed the reactions of carboaromatic anions with chlorocarbene [ 11 [2]. Following our studies of 4-azapentalenyl lithium (1) [3] [4], access to new simple heteroaromatic anions was desired. Our interest focused on dipyrrolo-2 H-imidazolyl lithium (2). Surprisingly, this simple analogue of the fluorenyl system as well as its parent compound, dipyrrolo-1,2 c : 2', 1 'el-2 H-imidazole (3) or any derivatives thereof, were completely unknown. It is the purpose of this communication to show how the target anion (2) and other novel heterocyclic systems can be constructed in a few straightforward steps starting from pyrrole.