Trityl reagents

In addition to standard syntheses in solution, even the solid-phase version has been developed, using a polymer-bound tritylation reagent [260-263]. With such temporary protection of the primary hydroxyl group, methyl 2,3,4-tri-O-benzoyl-a-D-gluco-pyranoside has been prepared from methyl a-D-glucopyranoside [260, 261]. 

Preparation of the silylium ion was carried out through the abstraction of the hydrogen of the silane, following the Bartlett— Condon—Schneider hydride transfer reaction first reported in the silicon series by Corey (12,13). Trityl reagents having a weakly coordinating anion are generally used to fully convert the silane. 

Me3SiBr, CH2CI2, 0°, 8-9 h, 80-97% yield.This reagent also cleaves the acetonide, THP, trityl, and r-BuMe2Si groups. Esters, methyl and benzyl ethers, r-butyldiphenylsilyl ethers, and amides are reported to be stable. 

An 5-4-methoxybenzyl thioether is stable to HBr/AcOH and 12/MeOH. The latter reagent cleaves 5-trityl and -diphenylmethyl groups. 

The Npys group can be. cleaved reductively with BU3P, H2O or mercaptoethanol. It is stable to CF3COOH (24 h), 4 M HCl/dioxane (24 h), and HF (1 h). The related reagent, 2-pyridinesulfenyl chloride, has also been proposed as a useful reagent for the deprotection of the 5-trityl, 5-diphenylmethyl, 5-acetamidomethyl, 5-/-butyl, and S-r-butylsulfenyl groups, but this reagent is very susceptible to hydrolysis. ... 

Attempts to prepare 2-aminoazepinium salts by the action of trityl tetrafluoroborate on azepin-2-amines, e.g. 18, resulted in ring contraction to stable 2-azabicyclo[4.1.0]hepta-2.4-dienium salts, e.g. 3-(pyrrolidin-l-yl)-7-trityl-2-azabicyclo[4.1,0]hcpta-2,4-dicnium tetrafluoroborate (19), the valence isomers of 7-(dialkylamino)-3-trityl-3//-azepinium tetrafluoroborates 64 with Meerwein s reagent the 2-ethyl derivative (77%) is formed. 

The aziridine-2-carboxaldehyde 56 can also serve as synthon for the synthesis of sphingosines, which are important biomembrane constituents [64]. One possible route involves the addition of an alanate to the aldehyde. In a later stage of this synthetic plan the aziridine can be opened, either via the intermediacy of an oxazoline or directly with dilute acid. Unfortunately, the reaction of aldehyde 56 with a vinylalanate has a poor diastereoselectivity of 3 2. Therefore, an alternative approach was considered, namely one involving the addition of a vinylzinc reagent to the aldehyde thereby employing our N-tritylaziridinediphenyl-methanol 51 as the chiral catalyst. Gratifyingly, only one diastereomer was obtained. Reductive removal of the trityl function, acetylation of the hydroxy... 

The use of trimethylsilyl-based electrophilic catalysts with organosilicon hydrides also promotes the conversion of aldehydes into ethers and avoids the need to employ the potentially hazardous trityl perchlorate salt.314,334,338 One reagent pair that is particularly effective in the reductive conversion of aldehydes into symmetrical ethers is a catalytic amount of trimethylsilyl triflate combined with either trimethylsilane, triethylsilane, PMHS,334 or 1,1,3,3-tetramethyldisiloxane (TMDO, 64) as the reducing agent (Eq. 179).314 Either... 

The addition of chloride ion to the medium in the case of the trityl chloride reaction reduces the net rate by virtue of the back reaction to regenerate trityl chloride. The product composition in the presence of various added reagents is a quantitative measure of the relative reactivity of the added reagents towards the carbonium ion. The results are summarized in Table VI. 

In 1983, Prasad et al.12 first reported the condensation of chloromethyl polystyrene with /V-hydroxyphthalimide to give the ester, hydrazinolysis of which yielded the desired resin-bound hydroxylamine. However, the sole purpose of this reagent was to react with, and hence extract ketones from, a complex steroidal mixture, and its use for the solid-phase synthesis of hydroxamic acids was not explored. Recently, the exploitation of the above solid-phase approach for the synthesis of hydroxamic acids was independently reported by three groups,7-9 all of which differ only in the method for the initial anchoring of TV-hydroxyphtha-limide to an 4-alkoxybenzyl alcohol functionalized polystyrene or trityl chloride polystyrene. Subsequent /V-deprotection was... 

Adition of Grignard reagents. Reaction of 2,3-O-isopropylidene-D-ribose (62) with ethynyl magnesium bromide gives l,2-dideoxy-4,5-0-iso-propylidene-D-a//o-hept-l-ynitol (63), which is then converted into its 7-O-trityl ether (64). Treatment of 64 with TsCl/pyridine provides 2,3-0-isopropylidene-5-0-trityl-a-D-ribofuranosylethyne (65) which upon deprotection affords derivative 66 (Scheme 22).89... 

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