טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentChinkov Nicka
SubjectStereoselective Synthesis of Metallated Dienyl Derivatives
DepartmentDepartment of Chemistry
Supervisor Professor Ilan Marek


Abstract

In this research, new strategies for the creation of versatile metallated dienyl derivatives in a single-pot operation, along with a new synthesis of substituted allylmetal compounds have been developed. To meet these challenging problems, we have used zirconocene intermediate (known as Negishi reagent) for the isomerization of a remote double bond and in the same time for the transformation of a heterosubstituted alkene into stereodefined metallated dienes. The latters, once formed, were reacted with versatile electrophiles, to afford the products as a single isomer, demonstrating the synthetic potential of this approach. The formation of these units (both terminal and internal zirconated dienes) occurs stereoselectively, and is unlimited by the chain length and the substitution of the remote unsaturation. To establish the mechanism of this facile reaction, theoretical calculations have been carried out at the DFT level, elucidating a full mechanism of the isomerization-elimination sequence, which is composed of the following key steps: C,H-allylic activation, b-H abstraction, ring expansion and, finally, decarbozirconation, accompanied by the elimination reaction.

The formation of substituted allylmetal species still remains a challenging task for synthetic chemists. During our research, we were able to develop a new general route for the preparation of substituted allylzirconocenes. The abovementioned isomerization-elimination pathway was also found to be useful for the conversion of w-heterosubstituted alkenes, namely, w-alkenols, into substituted allylzirconocene species. The strategy is applicable for the alkyl substituents of different tether length.

We strongly believe that these new concepts will find large applications in synthetic organic and inorganic chemistry, expanding the boundaries of synthetic possibilities.