Bt-stabilized carbanions

The concept of Bt-stabilized carbanions appeared as early as 1992 (19920M1381), but the utility of the associated chemistry is best illustrated by reviews dealing with synthetic applications (1994AA31) and Michael additions of Bt-stabilized carbanions (1998CCC599). Interesting examples of the latter include the synthesis of heterocycles (1997JOC6210) and the derivatization of heterocycles, such as thiophene (76) with a,p-unsaturated esters (77) to form (78) (Scheme 21) (1997JOC6215). 

LDA). Furthermore, Katrizky and coworkers have achieved highly stereoselective synthesis of -stilbene by reaction of tosylhydrazones with benzotriazole-stabilized carbanion with the aid of organolithium [32,33] - see (5) - X = 1 -benzotriazolyl (Bt). This method can be compared with Julia-type olefination, in which aldehyde is the substrate in the place of tosylhydrazone. 

The stability of the BTFP sulfonyl carbanions generated with a variety of bases including LDA, KHMDS, phosphazene bases (P4-t-Bu) and KOH-TBAB towards auto condensation was studied. It was shown that the sulfone recovery from the respective anions was higher than recovery of BT and PT sulfones. 

Five years later, in 1996, Kociensky ef a. successfully applied this methodology in their synthetic approach to Rapamycin [135]. They took advantage of the aforementioned observations that stabilized BT-sulfonyl a-carbanions favored -selective olefination. However, when they performed the coupling of enal 227 with the meta-... 

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