Decomplexation iodine

Nucleophilic substitution. Carbon nucleophiles react with the Cr(CO)3 complex of indanc followed by oxidative decomplexation (iodine) to effect highly selective or exclusive substitution a to the ring junction. Similar but less pronounced selectivity obtains in reactions of the Cr(CO)i complex of 1,2,3,4-tetrahydronaphthalenc. Good but... 

Shortly after this reaction was reported, Hegedus found46 that imines undergo a similar insertion process. The products (251) are structurally very similar to the alkyne adducts (247), and decomplexation with iodine, followed by treatment with trimethylamine TV-oxide, afforded a variety of substituted pyridones in good yield. 

Intramolecular substitution for chloride or fluoride is particularly effective. Oxygen heterocycles with fused benzo rings are obtained from Cr(CO>3 complexes of fluorobenzene with an o-(hydroxyalkyl) side chain.39,60 For example, complexation of 3-(2-fluorophenyl)-l -propanol with [Cr(CO>3(pyridine)3] at 25 C in ether (promoted by BF3 Et20) followed by reaction in DMSO with excess potassium f-butoxide for 3 h at 25 C gave the chroman complex (14).60 The yield in the cyclization step was 75% and iodine decomplexation was quantitative (equation 12). Efforts to produce the dihydrobenzofuran under the same... 

Arenes usually undergo electrophilic substitution, and are inert to nucleophilic attack. However, nucleophile attack on arenes occurs by complex formation. Fast nucleophilic substitution with carbanions with pKa values >22 has been extensively studied [44]. The nucleophiles attack the coordinated benzene ring from the exo side, and the intermediate i/2-cvclohexadienyl anion complex 171 is generated. Three further transformations of this intermediate are possible. When Cr(0) is oxidized with iodine, decomplexation of 171 and elimination of hydride occur to give the substituted benzene 172. Protonation with strong acids, such as trifluoroacetic acid, followed by oxidation of Cr(0) gives rise to the substituted 1,3-cyclohexadiene 173. The 5,6-trans-disubstituted 1,3-cyclohexadiene 174 is formed by the reaction of an electrophile. 

Epimerization of alpha-configuration of 10 into a p-equatorial configuration through acidic treatment and decomplexation by iodine provided the pseudo enantiomeric form of D-glucose derivative 11 (5). Finally, 11 is converted into the hetero olefin 12 which then received a variety of nucleophiles by chelation control to accomplish the synthesis of segment C of TTM 13. 

Reaction of the ruthenium alkyl complexes with bromine or iodine also cleaves the ruthenium-carbon bond to form the alkyl halides in reasonable yield [Eq. (102)]. Attempts to decomplex the organic substrate using... 

For example, coupling of complexed aldehyde 31 with ethyl acrylate gave lactone 32 with complete diastereocontrol.52 Furthermore, Lewis acid-mediated epimerisation of lactone 32 allowed for the isolation of the alternative diastereoisomer 33. Subsequent decomplexation with iodine liberated the two enantiomerically pure lactones.52... 

Activation of aromatic compounds by transition-metal complexes was initially studied with Cr(CO)3 complexes. Nucleophilic addition of 2-lithio-l,3-dithianes to arene-chromium(O) complexes 185 followed usually by iodine-promoted decomplexation affords the corresponding 2-arylated 1,3-dithianes 186. The reaction of //-(toluene)- and (anisole)tricarbonylchromium (185) with compound 161 gave mixtures (52 46 and 10 90, respectively) of ortho and meta substituted derivatives (186) (Scheme 54)244. The meta directing effect was also observed (mainly better than 95%) with amino and fluoro substituted complexes245. 

The decomplexation of compounds of the type 7 is achieved with iodine or perbromide, respectively, in the presence of methylimidazole or a,a-bipyridyl14 and is a general reaction, hence phosphinidene complexes of this type can also be considered as synthetic equivalents of the free phosphinidenes. 

Decomplexation to liberate the organic ligand is usually achieved by oxidation of the metal employing hydrogen peroxide, iodine, CAN, or photolysis in the presence of oxygen. 

Decomplexation of ArCr CO)3. The chromium carbonyl complexes of arenes are useful for activation of the aryl group to nucleophilic attack (6, 28, 125-126 7, 71-72). Decomplexation has been effected with iodine or by photochemical oxidation with destruction of the expensive Cr(CO)3 unit. A more recent method involves reflux with pyridine to form Py3-Cr(CO)3 in yields of 70-100%. The pyridine complex in the presence of BF3 can be reused for preparation of ArCr(CO)3. Isomerization of 1,3-dienes. Ergosteryl acetate (1) is isomerized by chromium carbonyl to ergosteryl 83 acetate (2) in 81% yield. Under the same conditions ergosteryl 83 acetate (3) is isomerized to ergosteryl 81 acetate (4). 80th reactions involve isomerization of a cisoid diene to a transpid diene. In contrast iron carbonyl isomerizes steroidal transoid 3,5- and 4,6-dienes to 2,4-dienes. ... 

Intramolecular delivery of the alkynyl moiety in ion pair 24 or -chloride 25 via the Zn tether would lead stereo selectively to a-C-glycosyl compound 17. The Nicholas reaction [35] with triflic acid-induced isomerization [36] of the dicobaltohexacarbonyl complex of aUcyne 17 provides cleanly the corresponding /3-C-glucoside complex 18 (O Scheme 4). Decomplexation with iodine and acetylation then gives /3-C-disaccharide 19. 

Reaction of 1,4-benzodioxin with chromium hexacarbonyl gives a 41% yield of the > -arene chromium complex (62). Reaction of this complex with n-butyllithium forms a yellow solution of the aryllithium. Reaction of this with a range of electrophiles gives a series of 5-substituted derivatives in modest yield, which are readily decomplexed by iodine to form the useful 5-substituted 1,4-benzodioxins (63) <89TL5519>. 

Cobalt complexes of a-alkynylpyranosides undergo acid catalysed epimerisation by a mechanism involving an intermediate acyclic cation. The intermediate in this process may be trapped by nucleophiles to give derivatives which after suitable modification, may be induced to undergo thermodynamically controlled cyclisation to furnish dehydrooxepanes (Scheme 8) <94T12883>. Decomplexation may be readily carried out with iodine. 

A synthesis of the tetrahydroquinoline enediyne structure (6) of the antibiotic dynemicin involves condensation of a Co(CO)6-protected propargylic alcohol with an enol. Thus treatment of 4 with triflic anhydride and 2,6-di-r-butyl-4-methylpyridine in CH2CI2/CH3NO2 results in 5 in 52% yield. (Use of nitromethane is crucial for satisfactory results.) This product on decomplexation with iodine provides 6, which undergoes aromatization when heated to form 7. 

In the case of the AB-component sulfide contraction was followed by base induced elimination of the cyano function and iodination to give 101, whereas transformation of the lactam into the thiolactam function formed 103. The sulfide contraction procedure was once again applied to couple the dimeric moieties under the influence of Ni(C104)2 as a template, followed by decomplexation, recomplexation with Zinc(II) and base induced decyanodation to yield the linear tetracyclic lactam (104). Upon treatment with MeOTf, the precorphin (104) underwent an... 

A soln. of lithium naphthalenide in tetrahydrofuran added to a soln. of startg. bis(tricarbonylchromium) complex in 6 1 THF/HMPA at —78° under argon, the dark brown soln. stirred for 30 min, butyl bromide added at room temp., and the mixture decomplexed with iodine at —78° - product. Y 74%. With acyl halides the central double bond isomerises. F.e.s. R.D. Rieke et al., J. Org. Chem. 54, 21-4 (1989). 

By application of the recently developed Pt-templated macrocyclization protocol (see above) to the bis-phenanthroline-Cu(I) complex, an interlocked tris-metalated Pt(II)-Cu(I)-Pt(II)-catenate 4.61 was obtained from precursor 2.59. Elimination of the Pt comers with iodine under simultaneous C-C bond formation afforded Cu(I)-catenate 4.62, which represented the higher homologue of Cu(I)-catenate 4.58. In this case, due to the larger ring sizes (34-membered) decomplexation of the Cu(I) center was achieved by reaction with KCN and conjugated catenane 4.63 was isolated in pure form after chromatography (Scheme 1.56). Evidence for the interlocked stmcture of 4.63 came from NMR spectroscopy and tandem mass spectrometry [427]. 

The cleavage of the chiral auxiliary requires an oxidative decomplexation with bromine, chlorine, iodine, or cerium(IV) salts and others in the presence of water, alcohols, and amines yielding carboxylic acids, esters, and amides, respectively. In all cases, the stereochemical integrity of the newly created stereocenter is maintained, whereas the iron-based chirality is "sacrificed upon the decomplexation. For example, the decomplexation with bromine leads to a substitution of the acyl group by bromide under retention at the iron atom. However, the complex [(PPh3)(CO)(Cp)FeBr] is susceptible to racemization in solution [61]. 

Nucleophilic Substitution. Some carbon nucleophiles add to tricarbonyl(arene)chromium complexes to yield anionic ii -cyclohexadienyl complexes (2) (eq 8), which give the substituted arenes via decomplexation by oxidation with iodine. Protolysis of the intermediate cyclohexadienylchromium complexes (2) generate cyclohexadienes, and reaction with electrophiles generates either the arene chromium complexes or produces the acylated species. 

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