Heterocycles silver© oxide

According to a report by Japanese authors, oxazirane rings are also formed by the action of silver oxide on perhydro-nitrogen heterocycles, e.g., decahydroquinoline (10) [Eq. (5)]. ... 

An extension of the research on silver complexes with Lewis base-functionalized mono(A-heterocyclic carbene) ligands has been made toward the better-studied and stronger coordinating phosphine systems. The reaction of a diphenylphosphine-functionalized imidazolium salt with silver oxide in dichloromethane affords a trinuclear silver carbene complex 50, as confirmed by electrospray-ionization mass spectrometry.96,97 Metathesis reaction of 50 in methanol using silver nitrate gives 51 in 33% yield. The crystal structures of 51 were found to be different when different solvents were used during crystallization (Scheme 12).97 One NO3- anion was found to be chelated to... 

Hydrazones of thiochroman-4-ones are converted into thiochromans under Wolff-Kishner-Huang conditions65 and into the azo dimers by silver oxide.66 Fisher indolization of the phenylhydrazones (33) gives 6,ll-dihydrobenz[6]indolo[2,3-d]thiopyrans (34), which by hydride loss form the thiopyrylium salts (35), or on dehydrogenation produce the pseudoazulenes (36) (heterocyclic analogs of the carcinogen, benz[a]-carbazole), as shown in Scheme 6.87-73... 

Gronowitz and co-workers have coupled 2-tributylstannylpyridine (and three other stannyl heterocycles) with hetaryl bromides in medium yields the presence of silver oxide was found to be necessaiy to facilitate these reactions [101]. Gutierrez et al. [102] have coupled various hetaryltins with 5-iodo-2 -deoxyuridine in medium to good yields. 

A hydroxamoyl chloride reacts with a C—C double bond of a 1,4-quinone in the presence of silver oxide as base and oxidant. The chemistry of heterocyclic quinones has been reviewed [2947, 3650]. Addition of a nitrile oxide (review of reactions [B-43,2115]) across the a,i -double bond of a butenolide leads to a new fused isoxazole ring. Cycloheptatriene undergoes a [6 + 2]n-cycloaddition at the 2,7-positions when it is stirred at room temperature for 4 days with nitrosoben-zene [2875]. 

The C-2 selective oxidative C-H coupling of unactivated pyridines with heterocycles was achieved in the presence of Pd(OAc)2, phenanthroline as the ligand, a silver oxidant, and pivalic acid (eq 145). Moderate to good yields were obtained when heteroarenes, such as thiophenes, indoles, furans, indazoles, or xanthines, were coupled to p3uidine (or p3razine, quinoline, pyrimidine). Virtually no homo-coupling or other regioselective (C-3 or C-4) products were observed in the reaction. 

The same pattern of activity is maintained in a closely related analogue. Condensation of amino-sulfonamide 201 with aldehyde 202 affords the saturated heterocyclic system (203) oxidation with silver nitrate leads to the antihypertensive agent pazoxide (204). 49... 

Since the successful exploration of silver(i) oxide usage as a multifunctional precursor for the synthesis of silver(i) A-heterocyclic carbene complexes, there has been an increasing number of reports related to silver(i) A-heterocyclic carbene chemistry. Silver(i) oxide can act as a weak base to deprotonate imidazolium salts, generating the free A-heterocyclic carbene ligands in situ, which then forms the silver(i) carbene complexes readily. This reaction can take place in the presence of air and moisture, and as a result, no special treatment in regard to the solvents has to be undertaken. More importantly, its basicity is rather specific toward the deprotonation at the G2 position of the imidazole moiety. Exploration of using silver(i) carbonate as a milder precursor in place of silver(i) oxide has also been pursued, but longer reaction times are usually required. 

In view of the versatility of A-heterocyclic carbenes as ligands and their structural diversity in silver(i) coordination chemistry, an extension of the work to ligands with two or more carbene moieties was reported. A dinuclear silver(i) complex 52 (Figure 21) with an o-phenylenedimethylene-bridged bis(carbene) ligand has been synthesized in 66% yield from silver(i) oxide and the bis(imidazolium) salt.88 The reaction to synthesize 52 has to be carried out in... 

Pyridine-functionalized N-heterocyclic carbene Rh and Ir complexes have also been described as active precatalysts for C=0 bond TH. For example, Peris and coworkers observed the formation of metal hydrides by C—H oxidative addition of a pyridine-N-substituted imidazolium salt such as N-"Bu-N -(2-pyridylmethyl-imidazolium) hexafluorophosphate in the reaction leading to M-pyNHC complexes, that is [lr(cod)H(pyNHC)Cl] (58) [54]. Transmetallation from silver carbene... 

Intramolecular electron transfer in a stepwise manner from the amine substrate to die silver(III) center in a 1 2 complex, [Ag(OH)4] -iV,/V-dimcthylanilinc, has been observed.44 The kinetics of oxidation of some aliphatic, heterocyclic, and aromatic aldehydes towards bis(dihydrogentellurato)cuprate(III) and argentate(III) in alkaline medium have been studied.45 A negative salt effect was observed in the oxidation of aminoacetic acid by diperiodatocuprate(III) complex in alkaline medium.46 The oxidation of glutamic acid by thallium(III) perchlorate is catalysed by Ru(M), Os(III), and Nd(III) in a free radical mechanism and the rate is inversely dependent on [H+] concentration.47... 

The synthesis of 4,5-dicyano-l,2,3-trithiole 2-oxide (172) starts from sodium cyanide and carbon disulfide which via (170) gave the disodium salt of 2,3-mercaptomaleonitrile (171 M = Na). Treatment of the corresponding silver salt (171 M = Ag) with thionyl chloride yielded (172) <66HC(2l-l)l). Phenylsulfine (174), prepared in situ by dehy-drohalogenation of phenylmethanesulfinyl chloride (173), slowly decomposed in ether solution at room temperature to give cis- and trans-stilbenes, mms-4,5-diphenyl-l,2,3-trithiolane 1,1-dioxide (36) and a 5,6-diphenyl-l,2,3,4-tetrathiane dioxide (68JCS(C)1612). The mechanisms of formation of these heterocycles are obscure. 

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