Silver Carbonate Spotlight 375 Compiled by Igor Dias Jurberg Igor Dias Jurberg Was Born in 1984, in Rio De Janeiro, Brazil

SPOTLIGHT 3053

SYNLETT Silver Carbonate Spotlight 375 Compiled by Igor Dias Jurberg Igor Dias Jurberg was born in 1984, in Rio de Janeiro, Brazil. He This feature focuses on a re- obtained his PhD from École Polytechnique (2007–2010), Paris, under the supervision of Dr. Fabien Gagosz and Prof. Dr. Samir agent chosen by a postgradu- Zard, working on the synthesis of alkynes and new transformations ate, highlighting the uses and catalyzed by gold(I) complexes. Since 2011, he is pursuing post- preparation of the reagent in doctoral studies in the group of Dr. Nuno Maulide at the Max- current research Planck-Institut für Kohlenforschung, Mülheim an der Ruhr, working on the development of original pericyclic cascades and C–H functionalization strategies. Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany E-mail: [email protected] Introduction ver bis(trifluoromethanesulfonyl)imide, derived from the reaction of silver carbonate and triflimide (Scheme 2).2

Silver carbonate, Ag CO , is a odorless, yellow to yellow- O, 65 °C H

2 3 2

Ag CO 2 HNTf H OCO + ++ 2 AgNTf 2 3 2 2 2

grey powder poorly soluble in water. Upon heating, it 2 gradually decomposes to silver oxide, Ag2O, and CO2 Scheme 2 Silver carbonate can also be used for the preparation of close to its melting point of 210 °C. Silver carbonate is other useful silver salts commercially available, but can also be readily accessed through the reaction of cheaper silver nitrate with sodium Silver carbonate has found a myriad of different uses in 1

carbonate in water (Scheme 1). organic chemistry, notably as oxidizing agent (Fetizon’s

H O, r.t.

2 reagent), as catalyst for alkyne activation, as halogen

2 AgNO

CO Ag CO Na 2 NaNO

3 + + 3 2 3 3

2 scavenger and as base and/or oxidant of choice for various Scheme 1 Silver carbonate is easily obtained from silver nitrate and transition-metal-catalyzed reactions. Selected applica- sodium carbonate tions of silver carbonate in these diverse contexts will be presented here. Silver carbonate can also be used to prepare other silver salts. One such salt, particularly useful in catalysis is sil- Abstracts

(A) Oxidation of Alcohols:

CO Me Fetizon’s reagent (silver carbonate on celite) is known to be a mild 2

oxidizing agent capable of converting alcohols into aldehydes and ketones.3 Here, this reagent is applied in the complex setting of an O

4 enantioselective total synthesis of (+)-upial. The desired lactone 12 steps, 21% overall yield

was obtained from the corresponding lactol in excellent 94% yield.

two steps,

Ag CO on celite

2 3 50%

(5 equiv)

CHO

C H , 80 °C H

6 6 H

H H

O O O

O OH

(+)-upial 94%

(B) 5-Exo-dig Cyclization of Alcohols and Carboxylic Acids: OH O Alcohols containing a proximal acetylenic part5 and isoindolones Ag2CO3 (0.10 equiv) R 6 C H , 80 °C This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. containing g-acetylenic carboxylic acid moieties can be efficiently R 6 6 O O cyclized using a catalytic amount of Ag2CO3. racemic, 2 examples, 90–99%5

O CO2H Ag CO (0.05 equiv) 2 3 O N R PhMe, 80 °C N R

O O racemic, 7 examples, 74–100%6

SYNLETT 2011, No. 20, pp 3053–3054 xx.xx.2011 Advanced online publication: 29.11.2011 DOI: 10.1055/s-0031-1290086; Art ID: V38211ST © Georg Thieme Verlag Stuttgart · New York 3054 SPOTLIGHT

NHPh

′ ′ N

N The azeto[3 ,4 :2,3]pyrano[4,5-c]pyrazole skeleton holds potential +

–

N Cl N

interest as a b-lactamase-resistant antibiotic. An enantioselective O O H

Ph Ag CO (2 equiv)

3 route towards one member of this class was developed from the in- 2 H

dioxane, r.t.

tramolecular [3+2] cycloaddition of a nitrilimine and a proximal al- N N

O PMP

N PMP

kene. The nitrilimine was generated via chlorine abstraction from the O

PMP

7 O

parent hydrazonoyl chloride using silver carbonate. enantiopure, 60%

O (D) Halogen Scavenger; C–H Oxidation Strategy: O

In landmark work,8 a C–H oxidation strategy was employed for the +

synthesis of eudesmane terpenes. The syntheses of two of them, di-

1) MeCO Br (1 equiv) 2

CH , 0 °C hydroxyeudesmane and pygmol, feature as key steps the selective Cl 2 2

2) sunlamp

R O

bromination of the more reactive tertiary carbon from the isopropyl Br

R O H

sidechain, followed by a cyclization event assisted by silver carbon- O

CF CH NH

3 2

CF CH NH

2 ate. After hydrolysis of the cyclic carbonate formed, the correspond- 3

Ag CO (1.2 equiv),

R = H, 10 steps, 21% overall yield

ing diol is obtained in a very selective manner. 2

r.t.; then aq AcOH R = OH, 11 steps, 17% overal yield

LiOH

(10 equiv) R = H dihydroxyeudesmane

R O

43% (+ 39% starting bicycle) O

R = OH pygmol

R HO

52% (+ 30% starting bicycle) O enantiopure

(E) Halogen Scavenger: Aziridinium Ion Formation:

A chiral anion phase-transfer catalysis was established by taking ad- Ph

R Ph 3

Cl )-TRIP (0.15 equiv) S (

vantage from the low solubility of silver carbonate and the generally OR

R OH (4 equiv), Ag CO (0.6 equiv) 2

2 3

R 1

high solubility of (S)-TRIP salts in organic solvents. Silver carbonate R

N 4 Å MS, PhMe, 50 °C

Ph Ph

abstracts the chlorine atom to generate an aziridium phosphate ion O

9 R R

pair, whose chiral anion directs the enantioselective nucleophilic *

13 examples

racemic

aziridinium ring opening to afford the corresponding amino ethers in 50–95% yield

good yields and excellent enantioselectivities.10 90–97% ee

(F) Base/Oxidant for Decarboxylative Cross-Coupling:

CO H

An efficient, regio- and chemoselective palladium-catalyzed in- 2

Pd(TFA) (0.15 equiv)

1 2

R R 1 2

tramolecular arylation of benzoic acid derivatives by means of a R

CO (3 equiv) Ag

2 3

5% DMSO–1,4-dioxane

decarboxylation/C–H activation sequence using silver carbonate as O

150 °C

base and oxidant of choice has been described.11 14 examples, 39–85%

(G) Oxidant for Olefination–Michael Addition Sequence: O

* O

The use of dinuclear rhodium species [Cp RhCl ] as catalyst and Ar

2 2 *

[Cp RhCl ]

2 2 N

Ar Ag CO as oxidant allows direct access to Heck cross-coupled prod- N (0.04 equiv) N R

2 3 R

12 H

ucts without the need for prior arene functionalization. The styrene +

CO (2 equiv) Ag 2 3

MeCN, 110°C EWG product obtained undergoes spontaneous Michael addition under the racemic EWG

sealed tube

20 examples,

reaction conditions to afford the corresponding cyclized products in (2 equiv) EWG

good yields.13 45–95%

References (1) For a detailed protocol see: Xu, C.; Liu, Y.; Huang, B.; Li, (b) Lee, K. J.; Choi, J.-K.; Yum, E. K.; Cho, S. Y. H.; Qin, X.; Zhang, X.; Dai, Y. Appl. Surf. Sci. 2011, 257, Tetrahedron Lett. 2009, 50, 6698. 8732. (8) Chen, K.; Baran, P. Nature 2009, 459, 824. This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. (2) For a detailed protocol see: Vij, A.; Zheng, Y.; Kirchmeier, (9) This can be seen as a particular case of a more general R. L.; Shreeve, J. M. Inorg. Chem. 1994, 33, 3281. concept coined as asymmetric counteranion-directed (3) Tojo, G.; Fernández, M. Oxidation of Alcohols to Aldehydes catalysis. For a leading reference, see: Mayer, S.; List, B. and Ketones; Springer Science; Business Media: New York, Angew. Chem. Int. Ed. 2006, 45, 4193. 2006. (10) Hamilton, G.; Kanai, T.; Toste, F. D. J. Am. Chem. Soc. (4) Takahashi, K.; Watanabe, M.; Honda, T. Angew. Chem. Int. 2008, 130, 14984. Ed. 2008, 131. (11) (a) Wang, C.; Piel, I.; Glorius, F. J. Am. Chem. Soc. 2009, (5) Other examples using stoichiometric amounts of Ag2CO3 131, 4194. For an intermolecular version, see: (b) Zhang, have also been reported: Pale, P.; Chuche, J. Eur. J. Org. F.; Greaney, M. F. Org. Lett. 2010, 12, 4745. Chem. 2000, 1019. (12) For a leading reference in this area see: Murai, S.; (6) Rammah, M. M.; Othman, M.; Ciamala, K.; Strohmann, C.; Kakiuchi, S.; Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonoda, Rammah, M. B. Tetrahedron 2008, 64, 3505. M.; Chatani, N. Nature 1993, 366, 529. (7) (a) Del Buttero, P.; Molteni, G.; Pilati, T. Tetrahedron: (13) Wang, F.; Song, G.; Li, X. Org. Lett. 2010, 12, 5430. Asymmetry 2010, 21, 2607. In this same context, see also: