טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMasarwa Ahmad
SubjectZirconocene-Mediated and Catalyzed Ring-Opening Reactions
of Alkylidenecyclopropanes
DepartmentDepartment of Chemistry
Supervisor Professor Ilan Marek
Full Thesis textFull thesis text - English Version


Abstract

Metal-catalyzed cleavage of carbon-carbon bonds is a field of current interest since it can lead to the design of new, selective and efficient processes for the utilization of hydrocarbons. Although the activation of C-C single bonds of strained three-membered rings is a known process, the stereoselective carbon-carbon bond activation of alkylidenecyclopropanes, through transition metal catalysts have emerged only lately as an efficient tool for the synthesis of functionalized linear products. In this context, we have developed a new zirconocene-mediated ring opening of alkylidenecyclopropane under mild condition through a combined C-H allylic activation reaction followed by a selective carbon-carbon bond cleavage to give the bismetallated allyl-alkyl zirconocene species that selectively react with two different electrophiles with high regio-and diasterioselectivity.

The state of the art of these methodology would consist in the easy preparation of challenging enantiomerically enriched saturated hydrocarbons with a quaternary stereogenic center such as the simplest enantiomerically enriched (2S)-4-ethyl-4-methyl octane and (S)-[2H1, 2H2, 2H3]-neopentane.

In the course of this work, we have also developed a simple and selective metal-catalyzed ring-expansion reaction of substituted alkylidenecyclopropanes into enantiomerically pure  cyclobutene derivatives possessing quaternary stereogenic centers.

In addition, we have reported the preparation of enantiomerically pure alkylidenecyclopropanes upon the copper - catalyzed addition of Grignard reagent to alkylidenecyclopropanes as well as the preparation of heterosubstituted alkylidenecyclopropanes through a [2, 3]- and [3, 3]- heteroatom sigmatropic rearrangement. For an easy preparation of enantiomerically pure alkylidenecyclopropanes, we should start from enantiomerically pure cyclopropenylcarbinol. Therefore, we have also developed a kinetic resolution to obtain cyclopropenylcarbinol in high enantiomeric excess.