Reacción de metátesis en cationes heteroaromáticos. Síntesis de aza-, benzo- e indoloquinolizinios

Resumen

Heteroaromatic cations are a kind of heterocyclic compounds, that are structurally classified as azinium-/azolium- and quinolizium-type cations depending on the nature of the quaternary nitrogen and aromatic heterocycle. Thus, in azinium and azolium salts a nitrogen of an azine or an azole is quaternized whereas a bridgehead quaternary nitrogen is the common feature of the charged system in quinolizinium-type salts. These compounds have attracted attention in fields as natural products, fluorescent dyes, antitumoral compounds, DNA intercalators, topoisomerase and telomerase inhibitors, NLO materials and ionic liquids, inter alia. While azinium and azolium cations are easily obtained by alkylation of the corresponding heterocycles, a general methodology for the synthesis and functionalization of quinolizinium-type cations still remained as an elusive goal. Recently, we have reported a novel approach to both functionalize quinolizinium salts involving palladium-catalyzed cross-coupling methodologies and synthesize quinolizinium-type cations by Ring Closing Metathesis (RCM). In this PhD project presented in this report we describe a new approach to the quinolizinium system throughout of the ß bond disconnection. First we describe our studies on the synthesis of 1,2-dihydroquinolizinium, and quinolizinium by RCM reactions by using Grubb¿s and Hoveyda¿s catalysts (G-II and H-G). The 1,2-dihydro-1-azaquinolizinium cations, have also been obtained by a RCM reaction from N-vinyl aziniums salts, in the presence of the G-II and H-G catalysts. It is noteworthy that this is the first route that allows to synthesize a pyrimidine system by a RCM reaction. The 1,2-dihydro-1-azaquinolizinium derivatives previously obtained, were deprotected and oxidized to the corresponding 1-azaquinolizinium cations in good yields. Furthermore, we also proved benzo[a]quinolizinium cation can be obtained by two different RCM reactions involving C1-C2 and C3-C4 bond formations, from a 2-butenyl-1-vinyl isoquinolinium salt (in a 25% overall yield) and 1-butenyl-2-vinyl isoquinolinium salt (in a 11% overall yield) in the presence of the H-G catalyst. Finally, indolo[2,3-a]quinolizinium cation has been obtained by RCM from two different charged dienes involving a 1-vinyl piridinium salt (in a 4% overall yield) and a 2-vinyl-ß-carbolinium salt (in a 25% overall yield) in the presence of the H-G catalyst