Synthesis of azaindenes. The benzo[c]pyrazolo-[1,2-a]cinnolinium cation, a novel heteroaromatic cation

Generation of pyrrolo[2,1‐a]isoquinoline derivatives from N‐ylides: Synthetic control and structural characterization

“…In the case of the dihydro derivatives obtained previously [6,7] from isoquinolinium N-ylides, some investigations were carried out in order to establish their stereochemistry [6,7]. Thus, the stereochemistry of the dihydro derivative 10 obtained by the reaction of isoquinolinium salt 9 with DMAD (dimethyl acetylenedicarboxylate) in the presence of triethylamine in methylene chloride as solvent (Scheme 3) was assigned on the basis of NMR spectroscopy [7].…”

“…One of the most versatile synthetic strategies starting from isoquinoline is the 1,3-dipolar cycloaddition of their corresponding ylides [1,2e,2f, [5][6][7][8][9] with both acetylenic and olefinic dipolarophiles. Usually, the syntheses of pyrrolo[2,1-a]isoquinolines involve two distinct steps: In the first step, the isoquinolinium salts are prepared and in the second step these react with acetylenic or olefinic dipolarophiles in the presence of a base whose role is to generate the N-ylide in situ.…”

“…By using acetylenic dipolarophiles, dihydro derivative intermediates are obtained along with the aromatic target products. The stereochemistry of such derivatives is of interest from the mechanistic point of view and thus received some attention [6][7][8][9][10].…”

Pyrrolo[1,2-b]pyridazines. A revisit

“…One of the most useful methods for obtaining pyrrolopyridazine derivatives is the 1,3-dipolar cycloaddition between pyridazinium N-ylides and activated olefinic or acetylenic dipolarophiles. The synthesis of pyrrolo[1,2-b]pyridazines through 1,3-dipolar cycloadditions has been described in over 35 papers, using acetylenic, [68][69][70][71][72][73][74][75][76][77][78][79][80] olefinic, [80][81][82][83][84][85][86][87][88][89][90][91][92] as well as both acetylenic and olefinic dipolarophiles. [93][94][95][96][97][98][99][100][101][102][103] The advantages of the method consist of: a) the availability of the raw material, as pyridazinium salts are easily obtained from pyridazine or its derivatives and halogenated derivatives, and b) the pyridazinium N-ylide generation and the cycloaddition are performed "one-pot", and the cycloaddition does not require special reaction conditions.…”

“…The first synthesis of a pyrrolopyridazine derivative through the reaction between a pyridazinium N-ylide and an acetylenic dipolarophile (DMAD) was reported in 1967 by Farnum and co-workers. 68 Heteroaromatic N-ylides can be classified by the substitution degree at the exocyclic carbanion as unsubtituted, monosubstituted and disubstituted. In [3+2] cycloadditions pyridazinium methanide (R 1 =H) 37, 69 pyridazinium carbanion monosubstituted 38 and carbanion disubstituted 39 N-ylides [70][71][72][73][97][98][99] were used as dipolarophiles (Scheme 21).…”