Vinyl triflones

Vinyl triflones 636 Vitamins, synthesis of 833 VSEPR theory 34... 

Scheme 25. Fuchs allylation, alkenylation and alkynylation with allyl and vinyl triflones...

Xiang, J. and Fuchs, P. L. 1996. AUcenylation of C-H bonds via reaction with vinyl and dienyl triflones. Stereospecific synthesis of trisubstituted vinyl triflones via organocopper addition to acetylenic triflones. J. Am. Chem. Soc. 118 11986-11987. 

Triflones reacted with p-tolylsulfonyl azide in the presence of two equivalents of base (NaH/glyme) and afforded vinyl azides380. These azides were reduced with LiAlH4 to afford the corresponding amines and, upon treatment with triethyl phosphite, they gave ketones after hydrolysis381. 

Simple sulfonyl carbanions which do not contain additional carbanion-stabilising groups, e.g. carbonyl groups or heteroatoms, can be readily alkylated in high yield by modern techniques with the use of alkyllithiums and lithium amide bases. A number of allylic halides have been successfully used. In allylic halides, the halogen directly attached to the double-bonded carbon is relatively inert towards nucleophilic attack (Scheme 41). In this way, sulfones (96) can be transformed via desulfonation into vinyl halides (97) or into ketones (98) by hydrolysis (Scheme 41). In contrast to ordinary alkyl sulfones, triflones (99) can be alkylated under mildly basic conditions (potassium carbonate in boiling acetonitrile) (Scheme 42). The ease of carbanion formation from triflones (99) arises from the additional electron-withdrawing (-1) effect of the trifluoromethyl moiety. 

Fuchs has examined a number of additional alkynes. One in particular, silyl-substituted triflone 104, may prove most useful, as it provides silylated alkyne products upon reaction with suitable substrates [62c]. In general, attempts to functionalize triflones with other groups at the alkyne carbon or at propargylic positions were unsuccessful. Triflones with more remote functionality, including bis-acetylenes, gave useful reagents. Fuchs triflone methodology can also be extended to vinylation and allylation reactions (Scheme 23) [63, 64). 

Haloquinone (3-Iodovinyl triflone Captodative vinyl bromide... 

The initial product of conjugate addition to 1 is a sulfonyl-stabUized vinyl anion. This species can participate in subsequent reactions, particularly if an electrophilic center is present on the original nucleophilic moiety. An example of this reaction manifold is illustrated in eq 6. Dimethylformamide is believed to serve first as a nucleophile in the conjugate addition to triflone 1. The fonnamide then acts as an internal formylating agent leading to the production of 6. The amphiphilic reactivity of 1 has... 

Magar SS, Fuchs PL. Syntheses via vinyl Sulfones. 44. Bis-alkylation of dimetallated phenylsulfonylmethyl triflone-a N + 1 annulation strategy for synthesis of cyclic vinyl sulfones. Tetrahedron Lett. 1992 33(6) 745-748. 

---