Heterocyclic aryl species

In one additional example of the formation of C-arylglycosides from glycals, Ichikawa, et al.,65 illustrated the applicability of this chemistry to heterocyclic aryl species. Specifically, as shown in Scheme 2.4.15, tri-O-acetoxy glucal was treated with furan and borontrifluoride etherate. The result was a 54% yield of the desired C-furanoglycoside as a 1 1 anomeric mixture. 

Lautens reported a new enantioselective Rh-catalyzed domino reaction that gives access to fused heterocycles 122 by desymmetrization of alkyne-tethered cyclohexa-dienones 120 [40]. The syn addition of the Rh-aryl species 124 onto the alkyne led to two new C-C bonds and two stereocenters with good enantioselectivity (Scheme 11.25). 

Sulfur characterization in coal by XANES was also carried out by Kasrai and coworkers [139], using as fingerprints the spectra of model compounds alkyl and aryl sulfides and disulfides and heterocyclic sulfur species. 

A new enantioselective Rh-catalyzed domino transformation of boronic acids with a cyclohexadienone-tethered alkyne gave access to fused heterocycles by desymmetrization of alkyne-tethered cyclohexadienones via the formation of two new C-C bonds and two new stereocenters with good enantioselectivities, syn-addition of the rhodium-aryl species onto the alkyne (130L1148). 

Intramolecular arylation of G-H bonds gives cyclic aromatic compounds. In this intramolecular arylation, the carbon-palladium cr-bond is first formed by the oxidative addition of Pd(0) species and then the resulting electrophilic Pd(n) species undergoes the intramolecular G-H bond activation leading to the formation of the palladacycle, which finally affords the cyclic aromatic compounds via reductive elimination.87 For example, the fluoroanthene derivative is formed by the palladium-catalyzed reaction of the binaphthyl triflate, as shown in Scheme 8.88 This type of intramolecular arylation is applied to the construction of five- and six-membered carbocyclic and heterocyclic systems.89 89 89 ... 

Among other heterocyclic compounds, 5-aryl-2-thiatriazolylamino oxadiazoles have been prepared by diazotization of 4-oxadiazolyl thiosemicarbazides and screened against two fungal species for fungicidal activity <76abc759>. 

Another arylation method, in the case of nitrogen heterocycles, does not need a halogenated derivative but a heterocycle activated by triflic anhydride260,261 (reaction 22). Simple aryl halides usually do not react with phosphines and special methods therefore have to be used for their arylation. The most widely used is the complex salt method , in which an aryl halide is heated with a phosphine in the presence of a transition metal such as nickel (II)2e (reaction 23). The catalytic cycle probably takes place by means of a reduced nickel(I) complex, generated in situ from the starting nickel(II) salt this nickel(I) species could undergo an oxidative addition of the aryl halide to yield a transient nickel(III) adduct, which after the reductive elimination of the aryphosphonium affords the recovery of the first active-nickel(I) complex (reaction 24). 

Several aromatic and heterocyclic acyl trimethylsilanes have been used as acyl anion equivalents by treatment with fluoride ion (Scheme 81, path a)23 133 154b160191192. Provided that the acyl substituent is electron-withdrawing, and that there are no aryl substituents on the silicon atom, acyl anions can be trapped by various electrophiles in moderate to good yields indeed, acyl anions and pentacoordinate silicon anionic species have both been detected in gas-phase reactions of acyl silanes with fluoride ion193. 

The sulfur-heterocyclic compounds in the mid-distillate range are primarily the thiacyclane derivatives, benzothiophene derivatives and dibenzothiophene derivatives. with lesser amounts dialkyl-, diaryl- and aryl-alkyl sulfides. Sulfur compounds are significant contributors to the vacuum gas oil fraction (Ma et al., 1997). The major sulfur species are alkyl benzothiophene derivatives, dibenzo-... 

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