[7783-93-9] · AgClO4 · Silver(I) Perchlorate · (MW 207.32)
(cyclization, dehydration, glycosylation, rearrangement of strained systems, solvolysis of halides)
Physical Data: mp 486 °C (dec); d 2.806 g cm-3.2
Form Supplied in: white crystalline anhydride; white crystalline monohydrate [14242-05-8].
Purification: dissolve 1g of the monohydrate per 6mL of benzene and heat at reflux under Dean-Stark conditions until the water is removed. Allow to cool and dilute with 4 mL of pentane per gram of the perchlorate. Filter the precipitate and place it in a desiccator containing P2O5 under high vacuum (1 mmHg) for 24 h.4
Handling, Storage, and Precautions: the anhydrous crystal readily forms the monohydrate, which is stable up to 43 °C and therefore should be stored in a desiccator. The salt is irritating to the skin and mucous membranes, corrosive, shock sensitive, and can be explosive in the presence of organic compounds.3,4
The thiophilicity of silver perchlorate has been exploited in two types of cyclization processes. Nicolaou and co-workers5 have developed a thioacetal cyclization strategy for oxocene synthesis that employs a silver perchlorate-sodium bicarbonate system to effect the transformation (eq 1). This protocol shows a marked increase in efficiency over other methods of oxocene construction. Similar tactics have been applied to the macrolide ring closure in eq 2 by Nimitz and Wollenberg,6 and to the synthesis of the BCD ring framework of brevetoxin A developed by Nicolaou and co-workers.7
Various secondary and tertiary alcohols can be efficiently dehydrated to their corresponding alkenes by the action of silver perchlorate in refluxing benzene,8 as a milder alternative to treatment with strong acid. It has also been demonstrated that a-hydroxy thioacetals9 (eq 3) and a-hydroxy ketones (eq 4)10 are easily dehydrated to cyclopentenones by this reagent in the presence of water and under anhydrous conditions, respectively. In the investigation of a-hydroxy thioacetals, silver perchlorate was demonstrated to be a very potent reagent for the cleavage of thioacetals to ketones.
Silver perchlorate has been employed in a large variety of ways to form glycosidic linkages.1c,d In concert with various Lewis acids,11,12 silver perchlorate catalyzes the glycosylation of 1-O-acetyl-D-glucose to produce a glucoside with a high degree of stereoselectivity (eq 5). Similar success has been achieved in both the stoichiometric and catalytic coupling of glycosyl fluorides,13-22 dimethylphosphothionates,23 and imidazolylcarbonyls24,25 with various silver perchlorate systems.
Rearrangements in a wide range of strained molecules can be triggered by silver perchlorate.1a,b Bicyclobutanes are readily transformed into butadienes26,27 in high yield, as evidenced in eq 6; cyclopropanes, particularly those in quadricyclane structures, display similar reactivity (eq 7).28-30 Padwa et al.31 have demonstrated that cyclopropenes can be manipulated by Ag+ into interesting structures (eq 8). Silver perchlorate has also been implemented in the rearrangement of propargyl acetates to allenes.32 Hiyama33 used a modification of this procedure to access protected substituted furanones (eq 9) that are complementary to those formed by the mercury-catalyzed process. Finally, 2-(trimethylsiloxy)allyl cations have been generated in the presence of silver perchlorate and furan to generate 4-pyrones via a [3 + 4] cycloaddition process (eq
Wynberg35 and colleagues have observed an interesting Tin(II) Chloride-Silver(I) Perchlorate.
James C. Lanter The Ohio State University, Columbus, OH, USA
Solvolysis of Halides.
quasi-Favorskii rearrangement when they treated 4-bromoadamantanone with silver perchlorate in acetone-water (eq 11); solvolysis with retention is observed, however, in the case of trans,trans-2-bromodecalin in refluxing acetonitrile (eq 12).36 Finally, Reese et al.37 have examined the silver perchlorate-facilitated methanolysis of dihalocarbene adducts in the context of synthetic routes to functionalized medium-ring cycloalkanes.
Wynberg35 and colleagues have observed an interesting
Tin(II) Chloride-Silver(I) Perchlorate.
James C. Lanter
The Ohio State University, Columbus, OH, USA