Transition Metal Catalyst Free Synthesis of Olefins from Organoboron Derivatives.

Stereoselective preparation of highly substituted olefins is still a severe challenge that requires well defined elimination precursors. Organoboron chemistry is particularly suited for the preparation of molecules with adjacent stereocenters. As organo boron substrates with leaving groups in β-position can undergo stereospecific syn- or anti-elimination, this chemistry harbors great potential for the synthesis of complex olefins. In recent years three main strategies emerged, which differ in their approach to the β-functionalized organoboron elimination precursor. (i) Stereoselective preparation of such elimination precursor can be achieved by addition of a boron-stabilized anion (d ) to an aldehyde or ketone (a ) or diastereoselective 1,3-rearrangement of suitable boron-ate-complexes. Stereospecific methods rely either on (ii) diastereospecific 1,2-metalate rearrangement of boron-ate-complexes that involve opening of appropriate heterocycles or (iii) addition of chiral carbenoids (d *) to chiral boronates (a *) with a leaving group in α-position.