Alkenes, synthesis from tosylhydrazones

Alkene synthesis. A modified version of an earlier synthesis of alkenes from the tosylhydrazones of aldehydes and certain alkyllithium reagents (9, 472-473) employs the N-r-butyldimethylsilyl derivatives (1) of tosylhydrazones of a,f)-enals, which undergo only 1,2-addition of an alkyllithium at - 78°. The adducts (2) decom-... 

Abstract In this chapter, alkene synthesis based on the reactiOTi of //-tosylhydrazones is described. The reactivity of tosylhydrazones is determined by either the acidity of a-proton and hydrazcMie proton or the electropositivity of the carbon of C=N bond. This leads to diverse reactivities and a series of N-tosylhydrazone-based olefination methodologies. Both non-catalytic and transition metal-catalyzed olefinations from Al-tosylhydrazones are introduced in this chapter. Most of the transition metal-catalyzed reactions proceed via metal carbene transformations. The synthesis of alkenes through Pd-catalyzed cross-coupling reactions of Af-tosylhydrazones is particularly attractive and will be discussed in detail. 

A general synthesis of fused methylenecyclopropanes employs the carbenoid ring contraction of bicyclic cyclobutanone tosylhydrazones, available from [2-1-2] cycloaddition of dichloro-ketene to alkenes. ... 

The conversion of ketone 38 to alkene 40 in the context of Winterfeldt s synthesis of (-)-myltaylenol was accomplished in two steps using classical conditions for the Shapiro reaction.22 The tosylhydrazone 39 was generated cleanly from 38 in near quantitative (98%) yield. Treatment of 39 with excess n-BuLi provided 40 in 90% yield. 

Indazoles were prepared by many different methods. Indazoles 41 were synthesized from nitroaromatics 39 and N-tosylhydrazones 40 with bases (14CC5061). A rhodium(III)-catalyzed oxidative olefination of 1,2-di-substi-tuted arylhydrazines with alkenes via sp C-H bond aaivation followed by an intramolecular aza-Michael reaction yielded indazoles (140L2494). Copper-catalyzed C-H amidation with aromatic imines 42 with tosyl azide provided a route to 3-substituted indazoles 43 (14OL4702). 4,5,6,7-Tetrahydro-lH-inda-zol-3-(2fJ)-one derivatives were prepared in two-step one-pot process (14SC1076). A regioselective synthesis of 2H-indazoles 45 was achieved using... 

Fig, 8 Synthesis of alkenes through coupling of heterocyclic tosylhydrazones with aryl halides, (a) reaction from hydrazone (b) reaction from ketone... 

---