Triflyl group

Other imidoylnitrenes in which the cyano group is replaced by mesyl or triflyl groups were also prepared but failed to promote the ring expansion 1-arylisoureas were the only products.166... 

Prior to Yamamoto s entry into this field, the scope of chiral phosphoric acid catalysis was strictly limited to electrophiUc activation of imine substrates. By designing a catalyst with higher acidity it was suspected that activation of less Lewis basic substrates might be possible. To this end, Yamamoto reported incorporation of the strongly electron accepting N-triflyl group [57] into a phosphoric acid derivative to yield the highly acidic N-triflyl phosphoramide 13 (Scheme 5.32)... 

The trifluoromethanesulfonyl (triflyl group) is one of the strongest electron-withdrawing groups and therefore is a versatile functionality for organic synthesis Trifluoromethyl sulfones have been prepared by using an electrophilic tnflyl source such as triflic anhydride or by displacing primary halides with a inflate salt... 

Protecting group manipulations allowed the introduction of a triflyl group at 06 to yield 271. The latter was treated with the trimethylsilylacetylene anion to give 272 in a yield of 76% over the two steps. 

More useful from a synthetic point of view than any of these variations is the discovery by Hendrickson that trifluoromethanesulfinate ( triflinate ) is a very effective leaving group in Ramberg-BScklund reactions. The reaction succeeds only if the precursors, a-triflyl sulfones, are fully substituted at the a-position if they are not, simple deprotonation occurs under the basic reaction conditions because the triflyl group is so strongly electron withdrawing. Consequently, this approach is applicable only to the syndesis of 1,1-di-, tri- and tetra-substituted alkenes. 

In the substrates shown in Table 1, the LG is attached to a primary carbon atom. The intramolecular displacement reaction is also possible when the LG is present at a secondary or tertiary carbon atom, see Table 2. Of particular note is entry 7 in Table 2 where a triflyl group serves as LG. 

Butanolides are ubiquitous subunits of a large number of bioactive com-poimds. Epoxy triflate sugars 1 and 2 open an easy access to selected polysubstituted chiral butanolides [36,37], by a two-step sequence. The first step is displacement of the triflyl group of 1 and 2 under extremely controlled conditions with a very reactive enolate of ferf-butyl acetoacetate followed by cycHzation under acid catalysis, which furnished 45 and 46 [36] (Scheme 9). 

The epoxide-assisted displacement of triflyl groups by fluoride ion is reported to be an efficient approach to deoxyfluoro-sugars. Benzyl 2,3-anhydro-4-0-triflyl-pyranosides undergo inversion at C-4 with tetra-n-butylammonium fluoride (TBAF) at room temperature in good yield thus treatment of the triflate (34-) with TBAF in benzene for 24 h gave the 4-fluoro-sugar (35) in 60% yield. The mild conditions avoid many of the difficulties encountered in fluoride-... 

The electron-withdrawal of the triflyl group also helps stabilize the corresponding ynamine derivatives. These can be prepared by coupling the lithium salt of AAbenzyltriflamide with an alkynyliodonium trifiate in a sequence which probably proceeds... 

Whilst direct displacement of the 2 -o-triflyl group in (26) could be effected, attempts to hydrolyse the anhydro-linkage resulted in formation of an unsaturated chloronucleoside (Scheme 8). ... 

---