Cesium fluoride, cleavage

A one-pot conversion of benzyl alcohols to benzyl fluorides by treatment of the alcohols with a combination of methanesulfonyl fluoride, cesium fluoride and 18-crown 6 ether in tetrahydrofuran has been repotted The reaction involves mesylation of the alcohols followed by cleavage of the resultant mesyl esters with a fluoride ion The reaction has been extended also to certain heterocycles bearing the N hydroxymethyl group [43] (equation 31)... 

The enantiomeric synthesis of rranj-3,4-disubstituted tetrahydrothiophenes using a sulfur ylide cycloaddition has been reported <990L1667>. The sulfur ylide derived from the action of cesium fluoride on sulfide 111 underwent an asymmetric cycloaddition with chiral a,p-unsaturated camphorsultam amide 112 giving tetrahydrothiophene 113 (80% de). The configuration was confirmed by cleavage of the chiral auxiliary followed by reductive desulfurization with Raney-Ni which gave known carboxylic acid 114. 

When exposed to chlorine monofluoride at — 78 CC, A4 S = N bonds undergo cleavage to form > SF2 and —NC12 compounds,94 but A6 S = N bonds readily add chlorine monofluoride at 50 C or, in the presence of cesium fluoride, at 25 "C without fragmentation.95... 

Cleavage with cesium fluoride was used in the case of stannylsilanes (equation 34)49. The generated stannyl anions are very effective in synthetic applications, mainly in abstraction of halogen to initiate organic 4 + 2 cycloadditions (equation 35)49, a reaction which constitutes one of its chemical characterizations. 

Oxalyl-CPG is obtained by reacting oxalyl chloride and 1,2,4-triazole with a 3 -hydroxyl nucleoside and LCAA-CPG. Cleavage of the oxalyl linker can be effected by a variety of mild reagents including triethylamine, propylamine-DCM, 5% ammonium hydroxide in methanol, or 0.5 M cesium fluoride in methanol for 15 min. Alternatively, 0.5 M DBU in either pyridine, dichloromethane, or dioxane was shown to effect full cleavage of the oxalyl linkage in less than 30 min at room temperature [111]. 

Fluoride ions induce a fragmentation reaction of SEM ethers resulting in loss of fluorotrimethylsilane, ethylene, and formaldehyde to give the deprotected alcohol (see section 1.2.4). However, compared with deprotection of ordinary silyl ethers, the reaction requires rather protracted reaction times, higher temperatures, or the presence of HMPA [Scheme 4.294]. Different combinations of fluoride source and dipolar aprotic solvent have been used. Deprotection of a SEM ether in a synthesis of Galbanolide [Scheme 4.295] was accomplished with tetraethyiammonium fluoride in hot DMSO whereas Ireland used excess cesium fluoride in HMPA at 115 C for 20 h to delete the SEM ether that completed the synthesis of Monensin [Scheme 4.296]. Fluoride-induced cleavage of a SEM ether in HMPA at temperatures as low as 45 has been re-ported. ... 

The carbonyl group of oxazolidinones undergoes a clean addition of Ruppert s reagent (trifluoromethyl trimethylsilane). jhe reaction catalyzed by cesium fluoride is quantitative (Eq. 24). The cleavage of the TMS ether (see p. 148 for other silyl group removal) liberates a-amino trifluoromethyl ketones. 

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