Triflates rearrangement reactions

Although deoxy sugars can also be formed directly from triflates by reaction with hydride reagents [Eq. (9) 19], molecular rearrangement [Eq. (10) 20] sometimes accompanies this pathway.)... 

Until the introduction of triflate or imidazylate esters in carbohydrates, SN2-displacements of carbohydrate sulfonates with charged nucleophiles in certain positions of hexopyranose orfuranose derivatives were not possible, or gave low yields of substituted products owing to the predominance of elimination or rearrangement reactions [6,22,32,33]. 

The efficiency of this rearrangement reaction suggests the possibility of an intramolecular version. Indeed, substituted vinylcyclopropyl trimethylsilyl ethers 37 containing a terminal dimethyl acetal underwent a surprisingly facile rearrangement to spirocyclobutanones 38 in good to excellent yields on treatment with trimethylsilyl triflate. 

The silver triflate-promoted reactions demonstrate the importance of the type of acid produced. There is a much weaker trend towards the a-glucosides with increased chloro substitution on the alcohol (decreasing its nucleophilicity), probably due to an increased rate of rearrangement of ion pair 3 into glucoside 5 by the strong acid. 

The silyl ketene acetal rearrangement can also be carried out by reaction of the ester with a silyl triflate and tertiary amine, without formation of the ester enolate. Optimum results are obtained with bulky silyl triflates and amines, e.g., f-butyldimethylsilyl triflate and (V-methyl-Af, /V-dicyclohcxylaminc. Under these conditions the reaction is stereoselective for the Z-silyl ketene acetal and the stereochemistry of the allylic double bond determines the syn or anti configuration of the product.243... 

Detailed investigations of the chemical reactivity of the diketiminato-stabilized phosphenium cations like 28 (Scheme 17) are to date rare and include only two reports dealing with the substitution and reduction of P-halogen-derivatives. Thus, reaction of 28 (X=Br) with sodium hydroxide in toluene was reported to proceed with displacement of the halide substituent at phosphorus and conservation of the heterocyclic ring to give a mixture of bromide and triflate salts containing a P-hydroxy-substituted cation, both of which were isolated in small yields [89], The products are remarkable as they represent one of very few examples of a stable phosphinous acid which does not rearrange to the tautomeric secondary phosphine oxide. Potassium reduction of the P-chloro-substituted derivative 34 produced the... 

Triflates also undergo Heck reactions and Gribble and Conway reported several such couplings of l-(phenylsulfonyl)indol-3-yl triflate (34) to afford 3-vinylindoles 224 [183]. Cyclohexene, allyl bromide, and methyl propiolate failed to react under these conditions, but triphenylphosphine afforded 225 in excellent yield (93%), and divinyl carbinol yielded the rearranged enal 226 (82% yield). 

Mdrour also explored the Heck reactions of indolyl triflates with allylic alcohols [139, 258]. For example, reaction of triflate 227 with allyl alcohol gives the rearranged allylic alcohol 228 [139],... 

Fig. 34 Approach to higher carbon sugars via the Wittig-type reaction Unusual rearrangement of the enone induced by triflate leaving group. 

More recently spinning disc reactors have been used by Wilson et alP0) to carry out catalytic reactions using supported zinc triflate catalyst for the rearrangement of a-pinene oxide to yield campholenic aldehyde. The results of this study, presented in Table 20.1, suggest that by using a supported catalyst on a spinning disc reactor it is possible to... 

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