Azafulvene dimer

Benz[e][ 1,2]azaborine, 1,2-dihydro-2-methyl-halogenation, 1, 656 Benz[6]- 1-azafulvenes dimerization, 4, 309 Benz[c]-2-azafulvenes dimerization, 4, 309 Benzazatropolone X-ray analysis, 7, 494 1 -Benzazepine, N-acetyl-6-hydroxy-bromination, 7, 528... 

Dubac has employed a Stille coupling reaction to synthesize the pyrroles 88 and 89 from stannylpyrrole aldehyde 87 [71]. The latter tin compound was prepared as shown, and related stannylpyrroles were synthesized similarly [72] or using Muchowski s 6-dimethylamino-l-azafulvene dimer lithiation methodology [73]. 

In addition to the protected pyrroles mentioned above, the 1-azafulvene dimer formed by Mannich reaction of pyrrole-2-carboxaldehyde with di-methylamine has also been successfully lithiated adjacent to both pyrrole nitrogens (Scheme 10). Reaction with electrophiles and subsequent hydrolysis leads to 5-substituted pyrrole-2-carboxaldehydes in good yield [88TL777 92JOM(423)173]. 

Other examples of N-substituted 3-bromopyrroles that have been successfully derivatized at the 3-position include either 4- or 5-substituted-3-bromo-l-tosylpyrroles 5 (90TL6785 91T7615) 3-bromo-l-tritylpyrrole 6 (91UP1) and the bromo-azafulvene dimer , which leads to 4-substituted pyrrole-2-carboxaldehydes 8 after reaction with electrophiles and hydrolysis (88TL3215). 

The recently reported dilithiation of the azafulvene dimer (20) is the key step in a synthesis of 5-sub-stituted pyrrole-2-carbaldehydes. This synthesis offers a reasonable alternative to the Vilsmeier-Haack formylation for the synthesis of such compounds. An example is shown in Scheme 26. 

Azafulvene, 6-aryl-6- N, N-dimethylamino-dimerization, 4, 309 1-Azafulvene, 6,6-bis(alkylthio)-synthesis, 4, 310 1-Azafulvene, 6-dialkylamino-reactions... 

The salts of methylene derivatives of 2H- and 3//-pyrroles and -indoles are produced in the Ehrlich reaction (Scheme 32, Section 3.05.1.2.8) and they are also intermediates in the Vilsmeier-Haack reaction (Scheme 24, Section 3.05.2.1.6). Although 6-fV,fV-dimethyl-amino-l-azafulvene, i.e. 2-(Ar,Ar-dimethylaminomethylene)-2//-pyrrole, dimerizes spontaneously (see Section 3.05.2.5), the 6-aryl-6-Ar)Ar-dimethylamino-l-azafulvenes (514 R = aryl) can be isolated (71JCS(B)1405) but, curiously, they are more susceptible to reactions with nucleophiles at the 6-position than are the corresponding salts (B-77MI30508). The benzo[6 ]-1 -azafulvenes, obtained from the reaction of 2-formylindoles with dialkylamines, also dimerize spontaneously, but the isomeric benzo[c]-2-azaf ulvenes, derived from 3-formylindoles, are thermally more stable, although they are extremely moisture sensitive... 

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