Ethers allylic, alkenylation with

The availability of trimethylsilane in larger amounts and reproducible quality by the reduction of chlorotrimethylsilane to trimethylsilane with magnesium hydride [91] in a milling reactor provided a better method in silane surfactant chemistry [92]. By using trimethylsilane in hydrosilylation reactions with a, 5-unsaturated compounds such as alkenols, allyl glycidyl ether, or alkenyl polyethers, a whole range of amphiphilic trimethylsilane compounds can be easily obtained (Fig. 8). 

Perfluoroallyl fluorosulfate is prepared by the treatment oiperfluoropropene with sulfur tnoxide m the presence of boron catalysts [2, 3, 4, 5, 6, 7] (equation 2) Perfluoroisopropyl allyl ether reacts similarly to give 58% polyfluoroallyl fluorosulfate in a cis/trans ratio of 6 4 [S] Sultones are the exclusive products without catalyst. Polyfluoroolefins such as 2-hydropentafluoropropylene [9], (2,3-dichloropropyl)tri-fluoroethylene [70], perfluoropropene [2, i], perfluoroisopropyl alkenyl ethers [S], and acyclic polyfluoroallyl ethers [77] undergo sulfur trioxidation to regioselectively produce the corresponding P-sultones in high yield... 

Intermolecular hydroalkoxylation of 1,1- and 1,3-di-substituted, tri-substituted and tetra-substituted allenes with a range of primary and secondary alcohols, methanol, phenol and propionic acid was catalysed by the system [AuCl(IPr)]/ AgOTf (1 1, 5 mol% each component) at room temperature in toluene, giving excellent conversions to the allylic ethers. Hydroalkoxylation of monosubstituted or trisubstituted allenes led to the selective addition of the alcohol to the less hindered allene terminus and the formation of allylic ethers. A plausible mechanism involves the reaction of the in situ formed cationic (IPr)Au" with the substituted allene to form the tt-allenyl complex 105, which after nucleophilic attack of the alcohol gives the o-alkenyl complex 106, which, in turn, is converted to the product by protonolysis and concomitant regeneration of the cationic active species (IPr)-Au" (Scheme 2.18) [86]. 

Palladium-catalyzed asymmetric cyclization/hydrosilylation tolerated a number of functional groups including benzyl and pivaloyl ethers as well as benzyl and methyl esters (Table 8, entries 1-4). Furthermore, the protocol tolerated substitution at one of the two /ra/zi -terminal alkenyl positions and at one of the two allylic positions of the 1,6-diene (Table 8). As was the case with diene cyclization/hydrosilylation catalyzed by achiral palladium... 

Metallated allylic ethers can also be used as partners in allylzincations of alkenyl-metals144. Allyl methyl ether could be metallated with s-BuLi in ether provided that TMEDA was present and, after transmetallation with ZnBr2, addition to the alkenyl-lithium derived from 205 proceeded slowly at room temperature. Nevertheless, after hydrolysis the corresponding allylic ether 227 was obtained with high diastereoselectivity (equation 110)146. 

Dehydrobromination of bromotrifluoropropene affords the more expensive trifluoropropyne [237], which was metallated in situ and trapped with an aldehyde in the TIT group s [238]synthesis of 2,6-dideoxy-6,6,6-trifluorosugars (Eq. 77). Allylic alcohols derived from adducts of this type have been transformed into trifluoromethyl lactones via [3,3] -Claisen rearrangements and subsequent iodolactonisation [239]. Relatively weak bases such as hydroxide anion can be used to perform the dehydrobromination and when the alkyne is generated in the presence of nucleophilic species, addition usually follows. Trifluoromethyl enol ethers were prepared (stereoselectively) in this way (Eq. 78) the key intermediate is presumably a transient vinyl carbanion which protonates before defluorination can occur [240]. Palladium(II)-catalysed alkenylation or aryla-tion then proceeds [241]. 

When 2-iodoalkyl vinylsilyl ethers 231 (Z=Si) were reacted with 224 in the presence of the Co(dppb)Cl2 catalyst, silatetrahydrofurans 232a (Z=Si) were isolated [294], When substrates 231 with substituted allyl groups (R3 and/or R4=alkyl) were treated with catalytic amounts of Co(dppe)Cl2 and 224 or phenylmagnesium bromide, a 5-exo cyclization proceeded and tetrahydrofurans 232c with exocyclic alkenyl units were isolated in 58-89% yield. For substrates with disubstituted alkene acceptors (R3=alkyl, R4=H), the formation of 18% of reduced tetrahydrofuran 232b was also observed [280, 295],... 

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