Pyrrolodiazines. 2. Structure and Chemistry of Pyrrolo[1,2-a]pyrazine and 1,3-Dipolar Cycloaddition of Its Azomethine Ylides

A new synthesis of the pyrrolo[1,2-a]pyrazine system from pyrrole is described. In light of the ab initio calculations carried out on this heterocyclic system some of its basic chemistry was investigated and included electrophilic substitution, addition of organolithium reagents, metalation with lithium diisopropylamide and subsequent reaction with electrophiles, and formation of salts by quaternization of the nonbridgehead nitrogen. N-ylides obtained from these salts undergo 1,3-dipolar cycloaddition with suitable dipolarophiles to give dipyrrolo[1,2-a]pyrazines, pyrazolo[1,5-a]-pyrrolo[2,1-c]pyrazines, and heterobetaines. Examples of intramolecular 1,3-dipolar cycloadditions are also reported.     

Synthesis of biaryls via intermolecular radical addition of heteroaryl and aryl bromides onto arenes

Tris(trimethylsilyl)silane (TTMSS) and azobisisobutironitrile (AIBN) promoted the easy intermolecular arylation of aryl and heteroaryl bromides under thermal conditions via a radical pathway.     

Efficient functionalization of quinolizinium cations with organotrifluoroborates in water

An efficient functionalization of the quinolizinium system is reported. The reaction of the four isomeric bromoquinolizinium salts with different organotrifluoroborates afforded alkyl-, vinyl-, aryl-, and heteroaryl quinolizinium derivatives in moderate or good yields. Reactions are carried out in water using a counterion exchange for the isolation of the cationic-coupled compounds.     

An improved synthesis of alpha-carbolines under microwave irradiation

[reaction: see text]. Alpha-carbolines are interesting core structures for designing DNA-interacting small molecules. However, these compounds are not commercially available and their synthetic methods are low yielding or time consuming. The shortest synthetic route, the modified Graebe-Ullmann reaction, has been optimized by using microwave heating in four different types of apparatus to give shorter reaction times and enhanced yields. Optimized conditions enabled the preparation of a small library of alpha-carbolines.     

Regioselective halogenation of pyridinium N-(benzoazynyl) aminides as a way to produce N-benzyl-α-aminobenzoazines

The halogenation of pyridinium N-(benzoazynyl) aminides with N-halosuccinimides provides a mild and regioselective method to functionalize the negatively charged diazine moiety in most cases. In some examples, however, formation of other products is explained. Finally, alkylation of the exocyclic nitrogen and reduction of the N–N bond provides a simple and straightforward strategy to obtain functionalized N-benzyl-benzoazynyl-α-amines.     

Reaction of imines with N-iodosuccinimide (NIS): unexpected formation of stable 1 : 1 complexes

Imines react with N-iodosuccinimide (NIS) to afford unexpected 1 : 1 complexes and the structure of one of these was determined by single-crystal X-ray diffraction; the reaction seems to be very general for substituted cyclic imines with solid stable complexes obtained in high yields; this is the first reported example of a halogen bonding interaction involving the C=N bond and NIS.     

Pyridinium N-2′-pyridylaminide: radical cyclization for the synthesis of benzonaphthyridine derivatives

The synthesis of benzonaphthyridine derivatives that incorporate a 2-aminopyridine moiety can be performed by intramolecular radical pyridylation of the appropriate substrates, obtained from pyridinium N-2′-pyridylaminide, using TTMSS and AIBN.     

Palladium-catalyzed arylation and heteroarylation of azolopyrimidines

A comparative study of the palladium-catalyzed arylation and heteroarylation of 5-bromoazolopyrimidines shows that aryl and electron-rich heteroaryl boronic acids gave higher yields than those obtained using the corresponding aryl and heteroaryl tributyl stannanes. In contrast, the reaction with electron-poor heteroaryl tributyl stannanes gave better results than the corresponding boronic acids.     

Enyne ring-closing metathesis on heteroaromatic cations

Cationic heteroaromatic enynes have been employed as substrates in enyne ring-closing metathesis, under an atmosphere of ethylene and using the Hoveyda-Grubbs catalyst, for the first time; the reaction affords new 1-vinyl- and 2-vinyl-substituted 3,4-dihydroquinolizinium salts, useful precursors for biologically relevant cations based on the quinolinizium system.