Fluoride ion mediator

Typically, oc,0-unsaturated esters, a,0-unsaturated aldehydes and a,0-unsaturated nitriles are poor acceptors for the Lewis acid catalyzed silylallylation procedure, but they are excellent acceptors for the complementary fluoride ion mediated allylation procedure (cf. Volume 4, Chapter 1.2, Section 1.2.2.1.7). Other suitable acceptors include 1,4-quinones,70 a,0-unsaturated acyl cyanides (162),718 silyl ot,0-enoates (163)71b and nitroalkenes (Scheme 26) 72 reduction (titanium(III) trichloride) of the intermediate nitronates arising from nitroalkene allylation affords y,8-enones (166). 

Other Examples of Fluoride Ion-Mediated Generation of Hyper-Valent Reagents... 

The reaction between diethyl phosphite and a-chloroketones can also be accomplished by fluoride ion-mediated deprotonation reaction in DMF (dry KF or KFTHjO as fluoride ion source), which constitutes anonbasic route to diethyl 1,2-epoxyalky Iphosphonates. Unfortunately, the application of this technique provides a mixture of 1,2-epoxyalkyIphosphonate (about 50%) and vinyl phosphate (about 30%) whatever the a-chloroketones. The reaction between 3-(co-bro-moacetyOcoumarin and diethyl or di- -butyl phosphite has been performed with 50% NaOH in CgHg under phase-transfer catalysis conditions with TEBA as catalyst. The only products of the reaction are the epoxyphosphonates isolated in 70% and 34% yields, respectively. In the presence of EtjN, diethyl phosphite reacts with 2-chloroacetoacetate to give diethyl 2-(ethoxycarbonyl)-l-methyl-l,2-epoxyethylphosphonate in 72% yield as a mixture of cis and trans isomers. ... 

Because of the available pentacoordinate state for silicon, fluoride ion and neutral fluorine in C—F bonds coordinate much more strongly to tetravalent silicon than to carbon, in spite of the comparable bond strengths of Si—F and C—F (132 kcal/mol). Therefore, most of the fluoride-ion-mediated reactions proceed via high valent silicate intermediates. The synthetic potential of the fluoride-ion-mediated reactions has been exploited in a number... 

Fluoride-ion-mediated generation ofbenzyne from silylaryl triflates (41) [20] is mild and excellent in chemical yields andsoithasbeen employed for a variety of electrophilic (42) [21 ], nucleophilic (43) [22], and cycloaddition reactions [23] (Scheme 3.26). N-Phenylations of sulfonamides (44), amines (45) [24], azirines [25], oxazoles [26], pyrroles [27], and imidazoles [28] with benzyne from 41 are also known. 

The approach generally only works well for electron-rich arenes, although for electron-deficient ones fluoride ion mediated cleavage can be used. Resins 44 [98] and 45 [99] are commercially available. They can be converted into the reactive halide or triflate form by treatment with HC1 in ether or TFMSA/DCM. Attach-... 

In contrast to this fluoride ion mediator effect, it has been established that bromosulfonium ions derived from sulfides and anodically generated bromonium ions can be used as so-called mediators for indirect anodic oxidations of alcohol. Therefore, it is interesting that the fluorosulfonium ions (G) also noticeably promote the anodic methoxylation. 

This novel fluoride ion mediated methoxylation is widely applicable as shown in Eq. 52. " Anodic oxidations of 2-ethoxycarbonyl-... 

A fluoride ion mediated condensation of the nitro sugar (14) with an aldehydo sugar, according to the method of Martin et al. [31], provides an expeditious route to a range of (3-linked-C-disaccharides (20). Here removal of the nitro group is achieved under radical conditions (Scheme 11.5). 

In an attempt to increase the water solubility of carborane - antibody complexes, the dialdehyde (23) and several other sugar aldehydes were treated with lithiated dicarba c/r o-dodecaboranes (29). The reactions were reasonably stereoselective, giving erythro- and tAreo-products, e.g., compounds (30) in ca. 4 1 ratios. From the same starting compound (23) the 1,6-C-linked disaccharide (33) was prepared by fluoride ion mediated condensation with peracetylated -C-glucopyranosyl nitromethane (31) followed elaboration of the... 

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