Deoxygenation of quinoxaline N-oxides and related compounds

The alkali induced deoxygenation of 3-(α-hydroxyalkyl)-quinoxaline-1-oxides is shown to be first order in substrate and in hydroxide ion. Examples are given to illustrate the synthetic utility of this reaction for the synthesis of quinoxaline and quinoline derivatives of type 4, 5, 8, and 11. The mechanism of the reaction is related to the mechanism of deoxygenation of heteroaromatic N-oxides by sodium dithionite.     

Synthesis and reactions of some heterocyclic azacyanines

The one-step reaction of some amino-substituted heterocycles with diiodomethane to give azacyanines is reported. This useful reaction is of wider application than initially reported and includes the synthesis of new substituted pyrido-, isoquino-, benzimadazo-, and benzothiazoazacyanines 7. Furthermore, treatment of these azacyanines with base generally affects a facile opening of the dihydrotriazinium ring resulting in the formation of new heterocycles 10, 11, and 12, which would be difficult to prepare by other means. This reaction takes an additional direction in the case of halo-substituted azacyanines 7b/c/d where treatment with base gives rise to new interesting derivatives of dipyridotriazines 14b/c/d.     

Facile syntheses of novel benzo-1,3-dioxolo-, benzothiazolo-, pyrido-, and quinolino-fused 5H-benzo[d]-pyrazolo[5,1-b][1,3]-oxazines and 1H-pyrazoles

A number of novel benzo-1,3-dioxolo-, benzothiazolo-, pyrido-, and quinolino-fused 5H-benzo[d]pyrazolo[5,1-b][1,3]-oxazines and 1H-pyrazoles were synthesized utilizing an easy and effective N,N-bond forming heterocyclization reaction. In so doing, the substrate scope of this heterocyclization reaction, which starts with o-nitroheterocyclic aldehydes, was expanded to provide several unique heterocyclic compounds for biological screening. This work further demonstrates the versatility of this simple, base-mediated, one-pot heterocyclization method in the construction of novel heterocycles.     

The structure of 2,3,5-trisubstituted 2-pyrrolin-4-ones

Compounds previously reported to be 2,3,5-trisubstituted 2-pyrrolin-4-ones are shown to have 5,5′-dimeric structures.     

Facile synthesis of furans from 2-ene-1,4-diones by diphosphorus tetraiodide

Diphosphorus tetraiodide effects reductive ring-closure of a variety of 2-ene-1,4-diones into furans within a few minutes at room temperature.     

Application of 1,2-diketones in the synthesis of phenazine oxides

Simple routes to phenazine oxides via 1,2-diketones are reported.     

Transannular Anti-Michael Addition: Formation of 4H-Pyrazolo[5,1-c]thiazines

The reaction of 2-(diphenylmethylene)thietan-3-one (2) with 1,2,4,5-tetrazines (3a-c) in KOH/MeOH/THF gives 4H-pyrazolo[5,1-c]thiazines (7a-c). This novel condensation reaction proceeds via the intermediacy of an 8-(diphenylmethylene)-2H-1,4,5-thiadiazocin-7(8H)-one (5), which undergoes a multi-step rearrangement including a rare anti-Michael addition.