[3058-33-1] · C19H15ClO4 · Triphenylmethyl Perchlorate · (MW 342.79)
Alternate Names: trityl perchlorate; triphenylcarbenium perchlorate.
Physical Data: mp 143 °C.4
Preparative Methods: perchloric acid is added to triphenylmethanol in acetic anhydride. The trityl perchlorate is separated, washed with ether, and dried.5
Purification: recrystallize from dry acetonitrile as yellow prisms.4
Handling, Storage, and Precautions: trityl perchlorate should be stored in the dark as exposure to light darkens the compound.4 It is rapidly hydrolyzed by exposure to moist air.4 All perchlorates present a potential explosion hazard.
Silyl enol ethers react with a,b-unsaturated ketones in the presence of catalytic amounts of trityl perchlorate (2-3 mol %1) to give 1,5-dicarbonyl compounds.6 No 1,2 addition products were obtained. It is possible to isolate the intermediate silyl enol ethers, which is not the case if Titanium(IV) Chloride is used as catalyst (eq 1).6 Anti Michael adducts are obtained preferentially with selectivities of up to >95:5 (eq 2).1 Silyl enol ethers of thioesters also react to give 5-keto thiol esters.7 Allylsilanes have been reacted with a,b-unsaturated ketones to give d,ε-unsaturated ketones (eq 3).8 1,4-Benzoquinones react with silyl enol ethers to give benzofurans.9 Trityl perchlorate was found to be a more effective catalyst for Michael addition reactions than other trityl salts.6
In the presence of a catalytic amount of trityl perchlorate (1-5 mol %), silyl enol ethers react with acetals to give b-alkoxy ketones (eq 4).10 Orthoformates react in a similar way.10 Aldehydes react with silyl enol ethers to give b-silyloxy ketones (eq 5).2 The reaction can be made threo selective, with selectivities of up to 82:18 reported.11 Alkyl enol ethers and acetals react in the presence of trityl perchlorate to give b-alkoxy ketones.12 A tandem Michael-aldol reaction has been reported which gives g-acyl-d-hydroxy ketones (eq 6).13
Perbenzylated 1-O-bromoacetyl-b-D-glucose reacts with alcohols in the presence of trityl perchlorate to give a-glucosides.14 a-Ribosides can be prepared in a similar manner.14 Other nucleophiles (silyl enol ethers, allylsilanes, and Cyanotrimethylsilane) react with benzylated 1-O-acetyl ribose to give a-C-ribofuranosides (eq 7).3
Christopher J. Urch
Zeneca Agrochemicals, Bracknell, UK