SILVER(I) NITRATE 1
Silver(I) Nitrate used for the hydrolysis of enol thioethers,10 tetrahydropyranylthio
ethers,11 S-t-butyl esters,12 and thiobenzoates,12 to the respective
alcohols, for the conversion of dithiobenzoates to S-benzoates,13
AgNO3
thioamides to amides,14 thioureas to ureas,15 and for the conver-
sion of orthothioesters to orthoesters.16
[7761-88-8] AgNO3 (MW 169.87)
Protection. Reaction rates for the conversion of the pri-
InChI = 1/Ag.NO3/c;2-1(3)4/q+1;-1
mary OH groups of nucleosides to the protected O-trityl
InChIKey = SQGYOTSLMSWVJD-UHFFFAOYAW
ethers with 4,4 ,4 -tris(4,5-dichlorophthalimido)trityl bromide
(mild oxidizing agent and Lewis acid used in a wide variety of
are considerably enhanced by the addition of AgNO3.17 AgNO3
chemical reactions)
is also used for the selective preparation of primary t-
ć% butyldimethylsilyl ethers by the reaction of nucleosides with tert-
Physical Data: mp 212 C; d 4.352 g cm-3.
Butyldimethylchlorosilane in MeCN.18 Yields in both reactions
Solubility: sol H2O, MeCN, alcohol, acetonitrile, DMF.
are high. AgNO3 is an effective agent for the conversion of several
Form Supplied in: white crystalline solid; widely available.
glucopyranoses to their 1,2-orthoacetates19 and as an agent for the
Handling, Storage, and Precautions: mild oxidizing agent; may
formation of glycosides20 (see also Silver(I) Nitrite).
be fatal if inhaled or swallowed; caustic and irritating to skin.
Ring Expansions, Contractions, and Rearrangements.
AgNO3-promoted rearrangements occur in numerous instances;
a few examples are given. Thus the 4-cyano-4,5-dihydroazepine
Original Commentary
in eq 2 gives the furo[2,3-b]pyridine on heating with an aque-
Duncan R. Rae
ous solution of AgNO3.21 Treatment of the N-chloroenolamine
Organon Laboratories, Motherwell, UK
in eq 3 with a threefold excess of AgNO3 gives the ²-lactam;
yields are about 50%, depending on the substituent used.22 The 1,
Deprotection. Silver nitrate is used as a deprotecting agent
1 -bishomocubane in eq 4, on treatment with AgNO3 in aqueous
for a number of functional groups. Thus S-trityl ethers are
methanol, rearranges to the pentacycle in quantitative yield.23
readily cleaved (AgNO3/Pyridine, 5 min, rt)1a to the thiol sil-
ver salts which are converted to the thiols on treatment with CO2Et
CN
EtO2C
Hydrogen Sulfide. The method has been applied to S-trityl ethers aq. AgNO3
EtO2C CO2Et
(2)
in nucleoside,1a peptide,1b and ²-lactam1c chemistry, although
53%
O
N
it is not always successful.2 Selective cleavage of an S,S-diaryl
N
H
phosphorodithioate in the presence of an O-dimethoxytrityl group
occurs using a large excess of AgNO3 (eq 1).3 Other deprotecting
Cl
AgNO3, MeCN
agents such as NaIO4, H2O2, and NCS are unsuccessful in this
R O
0 °C
N OH
N
process.3
R (3)
~50%
MMTrO MMTrO
Th Th
AgNO3
O O
rt, 20 h
(1)
100%
O O
(ArS)2P O P(OH)2
AgNO3, MeOH
O
(4)
rt
CO2Me CO2Me
Thioacetals,4 1,3-dithianes,5 and 1,3-oxathianes6 are con-
CO2Me CO2Me
verted, on treatment with AgNO3/ N-Chlorosuccinimide (or N-
Bromosuccinimide), to the corresponding ketones. The method is
specially useful when sensitive 1,4-unsaturated diones are
being liberated.5b Cyanuric acid can be used in place of NCS Dehalogenations. AgNO3 has been widely used for solvoly-
for the particularly difficult task of converting a diphenyl thio- sis with concomitant rearrangement of dihalocyclopropanes. Thus
acetal to its ketone derivative.7 Benzothiazoles are readily con- the trichlorocyclopropa[c]chromene in eq 5 gives the (dichloro-
verted, via their 2-lithio derivatives, to a variety of intermediates.8 methylene)chroman-4-one in 93% yield.24 Many other examples
Treatment of these derivatized benzothiazoles with Iodomethane are known. Dehydrobromination of the bromotetralone in eq 6
followed by Sodium Borohydride gives the corresponding with AgNO3 gives exclusively the endocyclic unsaturated ketone
N-methylbenzothiazolines, which are readily cleaved with in 90% yield; other reagents for this reaction give mixtures of the
AgNO3 in methanol to the corresponding aldehydes in high yields. exo- and endocyclic alkenes.25
This is a useful high yielding procedure for the preparation of Ä…,
²-unsaturated aldehydes.8 Cleavage of O-methylethoxymethoxy
O O
ethers (OMEM ethers) in the presence of a dithiane is accom-
AgNO3
Cl
(5)
plished by converting the OMEM ether to the O-isopropylthio-
aq. MeCN
methyl ether, which is then cleaved to the desired alcohol with
Cl
Cl O Cl
Cl
AgNO3 in the presence of 2,6-Lutidine.9 AgNO3 has also been
Avoid Skin Contact with All Reagents
2 SILVER(I) NITRATE
First Update
AgNO3, EtOH
rt
(6)
Kirsten Zeitler
Br Ph
90%
Ph University of Regensburg, Regensburg, Germany
O O
Introduction. With respect to its mild Lewis acidity silver
nitrate is widely used as a promoter and catalyst in organic synthe-
Solvolysis of arylmethyl halides with AgNO3 in hot aqueous
sis such as other silver(I) salts (AgBF4, AgClO4, AgOTf, AgOAc,
ethanol gives the corresponding alcohols,26 whereas a similar
etc.). For inducing different transformations (see below) the
reaction on alkyl bromides in MeCN is reported to be an exce-
reagent takes the advantage of its affinity for carbon-carbon un-
llent procedure for the preparation of pure nitrate esters.27 Benzyl
saturated bonds as well as to halogen and sulfur functional groups
dibromides are converted to the corresponding aldehydes in high
rather than oxygen functionalities.
yields,28 and Ä…-bromo ketones give high yields (>80%) of the
Based on its ability to complex with alkenes and alkynes, an
corresponding Ä…-diketones on treatment with AgNO3 in MeCN.29
additional useful application of AgNO3 is the impregnation upon
adsorbents (silica gel, alumina, Amberlyst resin, Sephadex, etc.)
Cycloadditions. The electrophilic nature of AgNO3 enables
and the use of the material for the so-called argentation chromato-
it to complex with alkynes and allenes, thus enabling intramolec-
graphy.39
ular cycloadditions to proceed. For example, treatment of a series
of phenolic keto-ynes (eq 7) with a catalytic amount of AgNO3
Deprotection. A selective removal of 2-S-trityl groups in
in methanol promotes cycloaddition to the triple bond in high
O-protected glycosides is possible in the presence of AgNO3/
yield.30 Similarly, Ä…-hydroxyallenes are rapidly converted to 2,
pyridine. From the thiolate silver salts the thiols are obtained
5-dihydropyrans on treatment with AgNO3/CaCO3 in aq acetone
on treatment with excess dithiothreitol (DTE).40 Mild hydrolysis
(eq 8).31
of dithiane-protected 2-alkylated Ä…-ketophosphonates is achieved
with AgNO3 in aq acetonitrile in the presence of bromine or NBS
AgNO3 (cat)
OH where several other methods failed, causing a concurrent hydro-
Ph
Ph O
MeOH, rt
lysis of the ketophosphonate.41 Dithiane deprotection in methanol
(7)
leads directly to the formation of the corresponding dimethyl
90%
O acetal.42 The high selectivity of AgNO3 for sulfur groups is illus-
O
trated by deprotection of a primary dimethoxytrityl (DMTr) group
from thiol in a methanolic buffer system; DMTr-protection at the
primary hydroxyl group remains untouched under these condi-
C7H15
OH tions (eq 9).43
AgNO3, CaCO3
MeO2C
aq. Me2CO, rt
(8) O
"
MeO2C
O
84%
C7H15
NH
1. AgNO3, NaOAc, MeOH
N O
O-DMTr
On extending the hydroxy alkyl chain from the allenic group by
2. DTE, NaOAc, MeOH/THF
two or three carbon atoms, cyclization results in the formation of
O
the corresponding Ä…-vinyltetrahydrofuran32 or Ä…-vinyltetrahydro-
pyran,33 respectively, both in high yields. In a similar man-
S-DMTr
O
ner, treatment of Ä…-, Å‚- and ´-aminoallenes with AgNO3 in
aqueous acetone gives the corresponding 2,3-dihydropyrroles,34
NH
Ä…-vinylpyrrolidines,35 and Ä…-vinylpiperidines,35 respectively, in
(9)
N O
good yields.
O-DMTr
O
Oxidative Couplings. Alkylboranes, formed on reaction of
terminal alkenes with diborane, dimerize on treatment with an
SH
aqueous solution of AgNO3/NaOH. Thus hexene gives a 66%
yield of dodecane,36 and the dienes 1,5-hexadiene and geranyl ac-
etate are converted to cyclohexane (66%) and trans-p-menthane N-Cyanomethyl groups can also be removed with AgNO3 in
(85%).37 Although the use of AgNO3/NaOH for these coupling refluxing ethanol.44,45
reactions is, to all accounts, equivalent to the use of Silver(I)
Oxide, oxidative cyclization is reported to be less successful when Protection. In ribonucleosides, AgNO3 in DMF can be used
this latter reagent is used. Oxidative dimerization of the dianions of for a simultaneous, selective protection of the 3 - and 5 -hydroxyl
Ä…,²-unsaturated carboxylic acids with AgNO3/THF gives mode- functions with di-tert-butyldichlorosilane in the presence of a
rate yields of the dienedioic acids, but the use of Iodine for this free 2 -OH in high yields.46,47 Acceleration of O-tritylation
coupling gives higher yields (40 80%).38 with dimethoxytrityl chloride (DMTrCl) is observed and can be
Coverage of the use of AgNO3/NaOH for oxidation of alco- used to circumvent migration reactions occurring by overnight
hols, aldehydes, etc., has not been included in this section as this treatments.47 Protection of sterically hindered OH-groups with
ostensively amounts to the use of Silver(I) Oxide. TBDMS-chloride can be assisted by silver nitrate.48,49
A list of General Abbreviations appears on the front Endpapers
SILVER(I) NITRATE 3
Ring Expansions, Contractions, Rearrangements. 1,3,4, -aldehydes to their corresponding furan derivatives.59 A com-
5-Tetrahydro-benzo[b]azepin-2-ones or 1,2,3,4-tetrahydro-benzo parative overview concerning the reaction of these sub-
[d]azepin-2-ones are accessible from simple tribromomethyl- strates with other metal salts or Lewis acid catalysts
substituted N-benzyl quinolines, or isoquinoline precursors via (HgClO4, PdCl2(MeCN)2, etc.) points out differences in product
a AgNO3-promoted ring enlargement.50,51 The reaction was used distribution.60
for the synthesis of the antianginal zatebradine (eq 10).
CO2tBu
AgNO3/silica gel
MeO
AgNO3
O
hexane
CH3CN/H2O 1:1
N
MeO
CBr3 Ph H
O
MeO
HO
CO2tBu
N (10)
Ph
MeO
O
O
MeO
(12)
A AgNO3-mediated skeletal rearrangement of a bromolactone
O
precursor is the key step for the synthesis of enantiopure bis(phos-
phinomethyl) norbornane ligands (eq 11).52
O
Me3Si
OH
Using less polar, hexane-based solvent mixtures61 more
AgNO3, MeOH
readily available alkynyl allylic alcohols can also be isomerized
Br CO2R
CO2Me
to the corresponding furans upon exposure to 10% AgNO3 on
O
CO2R
O
silica. Extension of this approach to alkynyl bromopropenoic acids
allows formation of Ä…-bromo lactones suited for further cross-
OR
coupling reactions.62 Cyclization of Ä…-alkynyl carbonyl substrates
(11)
proved to be an efficient method for the preparation of substituted
PPh2
furanopyrimidine nucleosides (eq 13).63
PPh2
R1
R1 O
O
Dehalogenations. Cycloaddition of tetrabromopropene with
AgNO3, acetone
NH
(13)
cyclic dienes yields polyhalogenated bicyclo[3.2.1]octadiene N
>95%
N O
derivatives which undergo rapid hydrolysis of the geminal dibro-
N O
mide to the corresponding ketone in good yield with an aqueous
R
R
solution of AgNO3. Conducting the reaction under anhydrous
conditions using AgBF4 in CH2Cl2 in the presence of diols
leads to in situ protected dibromoenones. The concept of Lewis
Intramolecular nitrogen attack in propargylated enaminones
acid-promoted conversion of carbon-bromine bonds to carbon-
allows silver-catalyzed access to functionalized pyrroles.64,65
oxygen bonds can be extended to the formation of carbon-carbon
This Ag-promoted hydroamination can also be used to ob-
bonds, i.e., arylations, in the presence of additional Ag2O as acid
tain N-bridgehead pyrroles.66 Silver nitrate-mediated cyclization
scavenger.53
of allenylamines, available from lithiated alkoxy allenes and
imines67 or through reaction of 1-(N-carbamoyl)-alkylcuprates
Cycloadditions. The Lewis acidic nature of AgNO3 enables
with propargyl substrates,68 provides access to 2,5-dihydropyrrole
activating complexation with alkynes, allenes, and alkenes, thus
derivatives. Iminoallenes can be used for the synthesis of substi-
permitting various cycloadditions to proceed. These Ag-catalyzed
tuted pyrroles in moderate yields in the presence of potassium
electrophilic cyclizations can either occur under oxygen or ni-
carbonate.69
trogen attack leading to the corresponding furan- or pyrrolidine-
Substituted isoquinolines can be obtained from ortho-alkynyl
based heterocycles.30,31,34
benzaldimines under mild conditions (eq 14).70
Allenoic acids can be converted to butenolides with catalytic
amounts of AgNO3/silica gel, a cyclization step which has been
t-Bu
N N
used for natural product synthesis,54,55 e.g., in the total synthesis
AgNO3, CHCl3, 50 °C
(14)
of the furanocyclic (-)-deoxypukalide (eq 12).56
R
A similar transformation with N-monosubstituted allenic car-
R
boxamides targeting lactams yields mixtures of imino dihydrofu-
rans and the desired pyrrolidones;57 whereas AgNO3-promoted
cyclization of Ä…-hydroxy allenes leads to 2,5-dihydrofurans,30,58 Less common are cyclizations of ²-allenic heterosubstituted
the same mild conditions allow conversion of allenyl ketones and systems to form the corresponding six-membered heterocycles.71
Avoid Skin Contact with All Reagents
4 SILVER(I) NITRATE
A silver-mediated, high yielding cycloetherfication was used as 4. Geiss, K.; Sevring, B.; Pieter, R.; Seebach, D., Angew. Chem., Int. Ed.
Engl. 1974, 13, 479.
one of the key steps for the construction of the dihydro-2H-pyran
5. (a) Corey, E. J.; Erickson, B. W., J. Org. Chem. 1971, 36, 3553. (b) Corey,
within the tricyclic framework of eunicins (eq 15).72
E. J.; Grouse, D., J. Org. Chem. 1968, 33, 298.
6. Frye, S. V.; Eliel, E. L., Tetrahedron Lett. 1985, 26, 3907.
O
O 7. Cohen, T.; Nolan, S. M., Tetrahedron Lett. 1978, 3533.
AgNO3
acetone
8. Corey, E. J.; Boger, D. L., Tetrahedron Lett. 1978, 5; 1978, 13.
HO
O
93%
9. Corey, E. J.; Weigel, L. O.; Chamberlin, R.; Cho, H.; Hua, D. H., J. Am.
Chem. Soc. 1980, 102, 6613.
10. Kejian, C.; Sanner, M. A.; Carlson, R. M., Synth. Commun. 1990, 20,
H
901.
O
11. Kruse, C. G.; Poels, E. K.; Jonkers, F. L.; van der Gem, A., J. Org. Chem.
O
1978, 43, 3548.
(15)
O
12. Shenvi, A. B.; Gerlach, H., Helv. Chim. Acta 1980, 63, 2426.
O
13. Hedgley, E. J.; Leon, N. H., J. Chem. Soc. (C) 1970, 467.
14. Barrett, C. G., J. Chem. Soc 1965, 2825.
15. Mechoulam, R.; Sondheimer, F.; Melera, A., J. Am. Chem. Soc. 1961,
83, 2022.
Halogenation Reactions of Alkynes. Silver nitrate can be
16. Breslow, R.; Pandey, P. S., J. Org. Chem. 1980, 45, 740.
used for the synthesis of haloalkyne derivatives in the presence
17. (a) Sekine, M.; Hata, T., J. Am. Chem. Soc. 1984, 106, 5763. (b) Sekine,
of NBS or NIS starting from either terminal alkynes or TMS-
M.; Hata, T., J. Am. Chem. Soc. 1986, 108, 4586.
protected acetylene derivatives.73,74 The high yielding reaction is
18. Hakimelahi, G. H.; Proba, Z. A.; Ogilvie, K. K., Tetrahedron Lett. 1981,
selective and shows a great functional group tolerance. For exam-
22, 4775.
ple, sterically more hindered C-silyl protected alkynes,75 O-silyl
19. Tsui, D. S. K.; Gorin, P. A. J., Carbohydr. Res. 1985, 144, 137.
protecting groups,76 esters, epoxides, and free-OH groups remain
20. Nashed, E. M.; Glaudemans, C. P. J., J. Org. Chem. 1987, 52, 5255.
untouched.74 Therefore, this method has been used in several total
21. Bullock, E.; Gregory, B.; Johnson, A. W., J. Chem. Soc. 1964, 1632.
syntheses. Haloalkynes are valuable synthetic precursors77 and
22. Wasserman, H. H.; Adickes, H. W.; de Ochoa, O. E., J. Am. Chem. Soc.
can be applied for direct coupling (e.g., Knochel s Cu/Zn chem-
1971, 93, 5586.
istry78 and the Nozaki-Hiyama-Kishi-Takai reaction79) or for the
23. Dauben, W. G.; Buzzolini, M. G.; Schallhorm, C. H.; Whalen, D. L.;
selective preparation of either E-76 or Z-vinyl halides,80 -boronic
Palmer, K, J., Tetrahedron Lett. 1970, 787.
esters81 or -stannanes.82 Furthermore, AgNO3- (or AgOTf) cat-
24. Brown, P. E.; Islam, Q., Tetrahedron Lett. 1987, 28, 3047.
alyzed chemoselective deprotection of trimethylsilyl acetylenes
25. Cromwell, N. H.; Ayer, R. P.; Foster, P. W., J. Am. Chem. Soc. 1960, 82,
in a mixture of methanol, water, and dichloromethane has been
130.
described recently.83
26. Aldous, D. L.; Riebsomer, J. L.; Castle, R. N., J. Org. Chem. 1960, 25,
1151.
Miscellanous Reactions. A reaction of acrylonitriles with
27. Ferris, A. F.; McLean, K. W.; Marks, I. G.; Emmons, W. D., J. Am. Chem.
nitrene generated by the reaction of chloramine T with AgNO3
Soc. 1953, 75, 4078.
in aprotic solvents affords 2-substituted aziridines in up to 44%
28. Buggy, T.; Ellis, G. P., J. Chem. Res. (S) 1980, 159.
yield.84 A more efficient method relies on catalysis with a unique
29. Kornblum, N.; Frazier, H. W., J. Am. Chem. Soc. 1966, 88, 865.
disilver(I) compound, generated in situ from AgNO3 with triden-
30. Jong, T-T.; Leu, S-J., J. Chem. Soc., Perkin Trans. 1 1990, 423.
tate 4,4 ,4 -tri-tert-butyl-2,2 :6 ,2 -terpyridine (t-Bu3tpy) with
31. Marshall, J. A.; Wang, X. J., J. Org. Chem. 1990, 55, 2995.
N-(p-toluenesulfonyl)iminophenyliodinane (PhI=NTs) as a ni-
32. Gore, J.; Audin, P.; Dootheau, A.; Ruest, L., Bull. Soc. Chem. Fr. 1981,
trenoid source to aziridinate simple olefins.85
313.
With the same silver catalyst, an oxidative intramolecular cy-
33. Gallagher, T., J. Chem. Soc., Chem. Commun. 1984, 1554.
clization of carbamates and sulfamates allows the generation of
34. Arseniyadis, S.; Gore, J., Tetrahedron Lett. 1983, 24, 3997.
N-heterocycles through amidation of CH bonds.86
35. Arseniyadis, S.; Sartoretti, J., Tetrahedron Lett. 1985, 26, 729.
Nitration of benzene derivatives in the presence of trifluo-
36. Brown, H. C.; Hebert, N. C.; Snyder, C. H., J. Am. Chem. Soc. 1961, 83,
roacetic anhydride has proven to be a successful detour via fol-
1002.
lowing reduction and Sandmeyer reaction if direct halogenation
37. Murphy, R.; Prager, R. H., Tetrahedron Lett. 1976, 463.
of aromatics is not possible.87,88
38. Aurell, M. J.; Gil, A.; Tortajada, A.; Mestres, R., Synthesis 1990, 317.
39. Williams, C. M.; Mander, L. N., Tetrahedron 2001, 57, 425.
Related Reagents. Zinc copper(II) Acetate Silver Nitrate;
40. Lipták, A.; Sajtos, F.; Jánossy, L.; Gehle, D.; Szilágyi, L., Org. Lett.
Silver Acetate; Silver Tetrafluoroborate; Silver Triflate.
2003, 5, 3671.
41. Afarinkia, K.; Faller, A.; Twist, A. J., Synthesis 2003, 357.
42. Coldham, I.; Crapnell, K. M.; FernÄ…ndez, J.-C.; Moseley, J. D.; Rabot,
R., J. Org. Chem. 2002, 67, 6181.
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