Oxidative heterocyclization

Reaction of thiolates with the l,2-dithiolan-3-one 1-oxide heterocycle of leinamycin generates the snlfenate intermediate Cyclization of this sulfenate onto... 

A new method for the synthesis of 1,2,3-thiadiazoles has been reported. The method starts with the thioanilide derivative 72, which is converted into the hydrazone 73. Oxidative heterocyclization by treatment with hydrogen peroxide gave exclusively the 1,2,3-thiadiazoline 74 (Scheme 8) <2003S2559>. 

The anodic functionalization of heterocycles, which generally results from a nucleophilic attack of reagents to the oxidized heterocycle, is of great interest in synthetic organic chemistry. In particular. 

In the 1990s, the groups of Hiemstra and Larock independently discovered that Pd(OAc)2 in DMSO serves as an effective catalyst for direct dioxygen-coupled catalytic turnover, and this catalyst system was applied widely to oxidative heterocyclization reactions. Examples include the addition of carboxylic acid, phenol, alcohol, formamide, and sulfonamide nucleophiles to pendant olefins (Eq. 26) [146-149]. 

The INOC strategy has been further extended to include a smaller class of cyclizations known as the intramolecular nitrile oxide-heterocycle cyclizations (INHC) in which the alkene component is either a furan or pyrrole (indole) unit. Typically, the furan adducts are more stable whereas the pyrrole adducts fragment (see (272) -> (273) -> (274)) (Scheme 51) (91JOC896). While the synthetic... 

An oxidative heterocyclization of phenylethynylphosphonic acid (74) with selenium dioxide was reported to occur upon heating of both components in dioxane in the presence of 48% hydrobromic acid [33]. Phosphonic acid 75 functionalized with a benzoselenophene moiety was the single isolated reaction product (30% yield). It was suggested that this heterocyclization occurs as shown in Scheme 8. 

Oxidative heterocyclization using hypervalent iodine 90S431. 

Dega-Szafran, Z., and Szafran, M., Complexes of carboxylic acids with pyridines and pyridine N-oxides, Heterocycles 37, 627-659 (1994). 

Oae, S., Ogino, K. Rearrangements of tert-amine oxides. Heterocycles 1977, 6, 583-675. 

Ethene (Ethylene) Cyclopentene have double bonds, . (e) Ethyne (Acetylene) has a triple bond Ethylene oxide heterocyclic (f)... 

Oxidative heterocyclization. Sulfur compounds undergo oxidation, and when the Ulfur atom is separated from a polymethoxylated aromatic nucleus by three, four, or five bonds, cyclization ensues (8 examples, 53-98%). 

Oxidative heterocyclizations. 2-Hydroxychalcones are converted into flavones. 2-(3-Hydroxypropyl) sugars undergo photoinduced oxidation to give spiroacetals with PhI(OAc)2-l2. 

Fia. 2. The PM3 fully optimized conformers of the 3-phenyl-1.2,3-oxathiazolidine 2-oxide heterocyclic molecular system. (Reproduced with permission from J. Heterocyd. Chem.)... 

Dehaen WH, Hassnta- A (1991) Cycloadditions. 45. Annulation of heterocycles via intramolecular nitrile oxide-heterocycle cycloadditirai reaction. J Org Chem 56 896-900... 

Reaction of heterocycles with a hydrazine residue at the a-position with sugars gave the respective hydrazones whose oxidative heterocyclization gave the 1,2,4-triazolo ring fused to the heterocycle. A variety of fused heterocycles such as pyridines, quinolines, triazines, and fused ring systems were prepared as acycHc nucleosides [2-5,109-111]. 

The decision to select the W-tosyl group for the N6 protection was made due to its ability to eliminate from a dihydropyridine, resulting in the formation of an equivalent of sulftnic acid, or its corresponding ester, as well as the oxidized heterocycle (a redox elimination). 

Oxidative Heterocycle Formation Using Hypervalent lodine(III) Reagents... 

The range of oxidative heterocyclizations was successfully extended to the construction of intramolecular C-O bonds. Zheng et al. [26] showed that enamides 29 can be oxidatively cyclized to functionalized oxazoles 30 using PIDA as an oxidant and BF3-OEt2 as a Lewis acid (Scheme 7 (1)). A similar strategy was adopted by Yu and coworkers portraying the synthesis of benzoxazoles in high... 

Besides carbon-carbon and carbon-oxygen bonds, a successful carbon-nitrogen bond formation was also achieved utilizing a similar oxidative heterocyclization of enolizable ketones. An efficient synthesis of tetramic acids with a pyrrolidine-2,4-... 

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